Why do cell membranes let small non-polar molecules through but won't let small polar molecules through? If the hydrophobic hydrocarbon chain of the phospholipid prevents the movement of polar molecules through the membrane. Why does the hydrophilic phosphate head of the phospholipid not prevent the movement of non-polar molecules?

The plasma membrane consists of hydrophobic and hydrophillic characteristics. Towards the outsides, they are hydrophillic, so they can create bonds with water. The insides are hydrophobic, allowing no water inside and keeping them tight together due to the polar forces.

An non-polar particle (if small), can pass through this because it does not interfere with the hydrophobic/hydrophillic (polar) nature of the plasma membrane. However, polar particles would not have the opportunity to move in, because the insides (hydrophobic) are literally afraid of water, or charges, don't allow polar substances to pass through.

So only hydrophobic (nonpolar), gases, and small particles (nonpolar) can pass through. There are exceptions of $H_2O$ passing through the membrane in small amounts because their electric charge is very minor.


Help explain multi alleles in terms of actual genetic code I understand that someones genetic makeup at an allele is usually denoted as (AA,Aa,aa).

That means that instead of an A-T pair you get a C-G pair on none, 1 or 2 copies.

Now, what exactly happens when you have a tri-allele (as in blood type). Are they looking at two base positions? Or is it instead of an A -> C mutation, you get something weirder like an A->G mutation (and thus you need to account for directionality) etc?

Thanks!

I understand that someones genetic makeup at an allele is usually
  denoted as (AA,Aa,aa).

No. That's what you learn in high school, because it's easy, and because it's what Mendel worked out for the 7 traits he studied in pea plants.  Real life is a lot more complex.  Most phenotypic differences cannot be explained in terms of exactly two alleles, one of which is classically dominant to the other.

  That means that instead of an A-T pair you get a C-G pair on none, 1
  or 2 copies.

Not necessarily.  Two alleles might differ at many many points in their sequence.

And you seem to be a bit confused about how people write out DNA sequence.  Even though DNA is a double helix, when we talk about what the sequence is, we refer only to one strand, like this

GAGCCATGGGGCGCCATGTTGCCACCAGCTGCCACGTGGCCTGGCTTTTGGTGCTGATCT

A mutation might turn that last T into an A, but we don't say "oh, nothing happened, it's still an A-T pair" because it matters which strand has which letter.

  Now, what exactly happens when you have a tri-allele (as in blood
  type).

Well, blood type is more complicated that just ABO...but here's a pretty old paper with some helpful details

http://www.ncbi.nlm.nih.gov/pubmed/2333095

"Here we present a molecular basis for the ABO genotypes. The A and B genes differ in a few single-base substitutions, changing four amino-acid residues that may cause differences in A and B transferase specificity.  A critical single-base deletion was found in the O gene, which results in an entirely different, inactive protein incapable of modifying the H antigen."


What Role Antagonists Play in the Study of Drugs? I am pretty unfamiliar to pharmacology. I'm doing a research on drug abuse, particularly opioids' mechanism of action. I encountered several times evidences that come from studies using antagonists especially naloxone that are to prove something is 'a specific opioid effect':

  Opioid-induced miosis in the human ... This action is a specific
  opioid effect as demonstrated by its antagonism by naloxone.

I wanted to know the rationale behind these kind of conclusions. Also an elaboration on the role antagonists play in drug research will be appreciated.

An antagonist is a substance that blocks a particular pathway (a receptor). You can therefore test whether a particular drug acts through the opioid system by using an opioid antagonist. If your substance still works despite the presence of the antagonist (which should block the opoiod receptors), you can conclude that it is not working thorough the opioid system.

Conversely, if your drug is blocked by an opioid antagonist, that is good evidence that your drug works through the opioid system.


can a protein recognized by antibodies not be immunogenic? I have a protein that is produced with the baculovirus system that is recognized by antibodies generated by immunization of rabbits with the same protein produced in E. coli. However the baculovirus protein did not induce an antibody response when I immunized some pigs.

Could it be that the baculovirus protein is not immunogenic? Even if the same protein is recognized by antibodies? If the rabbits produced antibodies with a protein that did not have post-translational modifications, how can not be immunogenic when the modifications are added?

Pure proteins are often poorly immunogenic because you need to have some kind of "adjuvant" effect to induce a strong effect. Bacterially-produced proteins may well have some bacterial LPS or other immune stimulants still present after purification which would drive a much stronger response than the same protein produced from eukaryotic cells. There are many other possible explanations -- one or the other protein may have aggregated or misfolded, which could drive a different response, for example.

In other words the effect you're seeing may be annoying but is not particularly shocking, and you have no choice but to do some routine troubleshooting at this point. Is your protein more immunogenic when administered with an adjuvant? Are the two versions identically folded? Are there antibodies present to a misfolded form that you're not detecting? And so on.


What is difference between "Syngonium" & "Pothos"? They both look the same to me, but they are different from each other.
Please help me in figure out the difference in both of these species.

Pothos is a common name for Epipremnum aureum, which, like the genus Syngonium, is in the monocot family Araceae.

From Wikipedia:

  E. aureum is an evergreen vine growing to 400 m (1,312 ft) tall, with stems up to 4 cm (2 in) in diameter, climbing by means of aerial roots which adhere to surfaces. The leaves are alternate, heart-shaped, entire on juvenile plants, but irregularly pinnatifid on mature plants, up to 100 cm (39 in) long and 45 cm (18 in) broad; juvenile leaves are much smaller, typically under 20 cm (8 in) long. The flowers are produced in a spathe up to 23 cm (9 in) long. This plant produces trailing stems when it climbs up trees and these take root when they reach the ground and grow along it. The leaves on these trailing stems grow up to 10 cm (4 in) long and are the ones normally seen on this plant when it is cultivated as a potted plant.

 Source: Wikipedia

Syngonium species, on the other hand, can have broader stems, stems that lose their chlorophyll, and different leaf shapes, to anme a few descriptions. From Wikipedia:

  juvenile leaves, whole ovate or elliptical; mature bisector leaves up to 11-secant and fan-shaped

Wikipedia also mentions some unique traits of this group of plants:

  The climbing stalks have elongated internodes and are elastic to some extent, however, after bending the stem's skin often breaks and peels off, turning brown or yellowish. The stem in section shows a distinct layer of the plant directly under the skin of the stem. The border between the colenchyma and stem stem is poorly scratched. In the parenchyma, starch grains are randomly distributed. The tissue of the stem also contains idioblasts with calcium oxalate crystals and drusen. The stem also contains secretory cells, containing tannins and milk juice, which solidifies in the air.


What is this grasshopper doing? I spotted a grasshopper standing on a pavement with a long sting placed in asphalt. I also recorded a video of it moving:

https://youtu.be/JoDdg2yUuYo

What is it doing?

It's its ovipositor & it's trying to dig a hole to lay its eggs.

  "How Do Grasshoppers Dig Holes to Lay Their Eggs? After breeding, female grasshoppers dig a hole in the ground in which to lay their eggs by using a special tube in their abdomen known as an ovipositor. The ovipositor is first used to dig the hole, and then to deposit the eggs one by one into the hole"

Probably not having much success on tarmac, did it eventually move onto soil?


Iron deficiency anemia symptoms explanation In my classes and on the internet, brittle nails and dry hair (or hair loss) are described as symptoms of iron deficiency anemia, but none explains the cause of such symptoms.

Does anyone have any clues or explanation of such symptoms?

http://en.wikipedia.org/wiki/Iron_deficiency_anemia#Signs_and_symptoms

The molecular basis of copper-transport diseases in Trends in Molecular Medicine, Volume 7, Issue 2, 1 February 2001, Pages 64–69, has a link to a 1973 paper by JM Gillespie entitled "Keratin Structure and Changes with Copper Deficiency," stating

  Menkes patients are often diagnosed from their unusual hair structure – termed pili torti – also known as kinky or steely hair, caused by reduced keratin cross-linking, a process that is catalyzed by an uncharacterized copper oxidase.

I haven't been able to find anything further, but since iron and copper levels can both be affected in anemia, this may be the link you're looking for. There may also be other enzymes involved that use iron-mediated catalysis. Since there are so many different kinds of keratins (the major protein that makes up hair and nails, among diverse other functions in the body), there may easily be multiple cross-linking and assembly pathways.

Other websites I found have also claimed that anemia-associated pathologies with hair and/or nails may be related to reduced oxygenation as a result of low iron levels, but they don't give any citations, and given the nature of the sites (nail care, fashion, etc.) it may just be an educated guess.


Is there a term for the group of individual organisms whose matrilineally descended female ancestors all share a common ancestor? A group of individual organisms that are all descended from a common ancestor is a clade. Is there a term for a group of individuals whose matrilineally descended ancestors (mothers, maternal grandmothers, maternal grandmothers' mothers, etc.) are all descended from a common ancestor?

I don't think there is a word for that.

However, you can refer to this specific DNA sequence as being exclusively maternally inherited (such as mtDNA for example; see also mtEve). For this sequence, the classical vocabulary from the field of phylogenetics and population genetics apply nicely.


Are there any species whose descendants can meet their ancestors from 100 generations back? I.e. Humans can sometimes meet even their great-great-grandparents, but are there any species that can be alive at the same time as their great-great-……-great-grandparents? I imagine it would be those species with a long lifespan and an early age of first reproduction.

Yes, cryopreservation works quite well for many species, including multicellular animals. So you can freeze the ancestor and wait until the descendant is there, then unfreeze them. A good recent example in the news would be the Siberian worms that woke up after being frozen in permafrost for a very long time.
Cryopreservation is routine in laboratories, to freeze ancestors and compare to descendants; see the Long Term Evolution Experiment. It doesn't work well for every organism of course. In principle it might work for humans.
Some bacteria will sporulate, and in spore form they can persist for thousands of years theoretically. They don't even need cryopreservation. There are other organisms that do something similar as well.


Evolution history of virus tracing How do biologist trace evolutionary history of virus, is there any article on this issue,
e.g. how scientist got to know that coronavirus evolved from bat or camel or pig?

The identification is done by sequencing virus samples and comparing them to reference genomes of viruses. By doing this, you can analyze how closely related an unknown virus is to the references.

For the nCoV this method shows it is 96% identical with a known bat coronavirus (see reference 1 for details).
As viruses accumulate mutations due to errors during replication, this method is also used to generate genetic trees of the virus to analyze how it spreads, map routes of infection and also if the virus has been introduced to humans more than once (reference 2 has a nice overview on this topic).

The problem here is: You need to have some known references for comparision, if you have a completely new virus which has never emerged before, this will not help. For this reason there are projects ongoing which collect samples to identify yet unknown viruses (see reference 3)

Discovery of a novel coronavirus associated with the recent
pneumonia outbreak in humans and its potential bat origin
DNA sleuths read the coronavirus genome, tracing its origins and
looking for dangerous mutations
Virome analysis for identification of novel mammalian viruses in
bats from Southeast China


Combination of different antibodies How can I know if I can combine anti Cenp-C and anti Rod1 antibodies? I want to use them to label those protein and analysing cells by fluorescence microscopy.

*Cenp-C is kinetochore protein and Rod1 is localized on the kinetochores or spindle microtubules during cell division.

Can I just combine them if they are from different animals? how can I know they will not have cross reactivity?

Thanks

If they are made in different animals you should be fine.  You could do a western with those antibodies though, to double-check.  Looks like Cenp-C is about 106kD and Rod1 is about 60kD.  So on a western, if you see bands at both those sizes with one of the antibodies, you have cross-reactivity between those proteins.  And if you just see the specific band you're looking for, you're good.


I am trying to identify this plant I am trying to identify this medium arching shrub growing to about 1.5m high x 2m wide in the subtropical climate of the Mt Coot-tha Botanic Gardens in Brisbane, Australia. Unfortunately there was no label with it. The inflorescence is about 3cm across, a greenish yellow, and made up of many tentacle-like florets.  I don't think it is an Australian native plant.

It looks like combretaceae, or a species related to it.


Do ants use something similar to the honey bee "waggle dance" to instruct the rest of the colony where to find a food source? In the 20 years since we built our home, we've just recently had our first ant infestation.

I'm familiar with the fact that ants leave scent trails to find their way back and forth between the colony and a food source.  So in my limited experience with ant eradication, I assumed that by taking away the empty ice cream bowl and scrubbing the scent trail which lead to it off the kitchen counter (multiple times with different household cleaning products) the ants would quickly give up their search.

My assumption was that the oncoming foragers would be confused by the abrupt end of the scent trail and wander aimlessly in the gap between where the trail had been scrubbed away and the former location of food.

However, what I’ve observed again and again is ants continuing to move across the scrubbed counter to the exact location of where the food used to be -- as if they didn't need the scent trail.  Their only confusion seems to be the lack of food at that spot.  This behavior will continue for several hours after the removal of whatever food had been there, despite multiple eradications and vigorous scrubbings of where the original trail had been.

Ants follow odor plumes to food sources according an answer in another Biology Stack Exchange post.
(Can ants sense food from a long distance?)

And from a link in the same Biology Stack Exchange post “If they [patroller ants] didn’t return to the nest, departing foragers would know it wasn’t safe to go search for food.” and “The ants can take advantage of sudden windfalls of food, but they don’t waste energy and resources if there’s nothing there.”
(https://wikkorg.wordpress.com/2015/04/23/ants-swarm-like-brains-think/)

Here are my questions:

Are ant scent trails strong enough to withstand multiple washings with soaps, detergents and disinfectants?

Can ants detect airborne food molecules in very small parts per million, even after the food and its odor plume have been removed?  If not, do ants use something similar to the honey bee "waggle dance" to instruct the rest of the colony where to find a food source?  Or both?

Why and how do they keep coming back to a place where there is no food, especially if (eradicated) members of the colony are not returning?

I can only help you on one question about if ants perform a similar communication such as the "waggle-dance" to tell other ants if there is food elsewhere?
Ants will send out scout ants or forages, which will go out in search for food. The ants will lay a pheromone trail, by tapping their abdomen on the ground, like breadcrumbs. If the ant has found a food source, they will taste the food and take part of the food and store it in their crop. The ant will take the food sample and re-trace her trail, making it more detectable when returning to the food source. Once the ant reached the nest and finds another ant, she will regurgitate the food from her crop and position it between her mandibles. She will go towards another ant and exchange the food and pass it on to the ant in a "kissing" motion. This is called trophallaxis, where there is a donor, the scout or forager ant, and a recipient, the ant back at the nest. The ants will then follow the trail the scout first put down and will eventually create a motoway of food going to the nest.
Look up people like Nigel Franks and John Sudd - The behavioural ecology of ants.
The lives of ants - Laurent Keller and Elisabeth Gordon
The Earth dwellers - Erich Hoyt
sciencedirect.com/science/article/pii/0003347295801405 about trophallaxis in solenopsis ants sciencedirect.com/science/article/pii/037663578290050X about trophallaxis in Myrmica ruba
Hope that helps.


Why does sunburn cause fever? Today I found out that sunburns can cause fever.

What I don't understand is how/why? In my understanding fever is the side effect of an immune reaction against an intruder, mainly bacteria (though I admit I can be wrong).

Google searches like "can sunburn cause fever" only bring up that it is possible, but not why.

Here is a good article on the topic.

https://www.nlm.nih.gov/medlineplus/ency/article/003227.htm

But it's most likely due to the fact that a sun burn is an actual burn on the skin that can cause inflammation, inflammation can in turn cause fever. Also having a really bad sunburn can open you up more to the possibilities of skin infections. If this happens then once again you might get a fever due to infection. If you really want to find out more on the cause of fever after sunburn you need to examine the pathophysiology of fever and why fever happens. I bet my money on fever due to skin inflammation after a sunburn, I guess the real question would be why does inflammation cause fever since sunburn = skin inflammation

Here is a good article

http://antranik.org/inflammation-and-the-pathophysiology-of-fever/


Origins of transcription factors and RNA Polymerase I was learning about transcription factors and RNA polymerase from Khan Academy to supplement Dr. Robert Sapolsky's lectures on Human Behavioral Biology. As I understand:

RNA Polymerase transcribes DNA to RNA
Transcription factors are proteins that help the RNA Polymerase bind or inhibit it from binding to the DNA and transcribe it to RNA
Transcription factors called activators help RNA Polymerase bind to the DNA
Transcription factors called repressors prevent RNA Polymerase from binding to the DNA

It seems like we need transcription factors and RNA Polymerase to express genes and produce their corresponding proteins. But transcription factors and RNA Polymerase are proteins themselves. Thus, they must have come from their own respective genes. This seems like a "chicken and egg" problem.

How did early organisms with genetic material get around this problem?

This is one of the main features of the RNA World.
What I mean by that is, RNA not only acts as a repository of genetic information, it also acts as an enzyme. This enzyme is known as Ribozyme. Ribozyme confers a self-replicating property to RNA, leading to the hypothesis that RNA might be the ancestor to the present day self-replicating genetic material.


A question related to qPCR analysis Here is the thing. I am using a method, called TU-Tagging, to isolate cell type specific RNA. You can find more about the method here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2783170/

To explain it very briefly, there is an enzyme called UPRT (Uracil Phosphoribosyltransferase) which is expressed in Toxoplasma gondii. Under normal circumstances UPRT creates UMP from host cells' uracil and this UMP incorporated in RNA. However, they found that this enzyme cannot distinguish uracil and uracil analog 4-Thiouracil (Basically has thio on 4th position of the uracil). So, when 4-TU provided externally, UPRT incorporates 4-TU into RNA and you get thio-RNA. Then with basic biotinylation and streptaividin isolation you can get thio-RNA from your total RNA isolate. (Of course UPRT should be put to specific cell types of your interest)

Anyway, after the explanation (maybe it was unnecessary though) here is my question.

After I isolate my so called specific RNA, I check the purity by qPCR by using cell type specific markers. I do not have a reference gene. The only thing I am interested in is the presence or absence of markers (and also the fold change of course). Now, I have some data but I do not know how to present them (There is nobody in my lab experienced with qPCR and my experience is just so limited).

Do you have an idea how I can overcome this issue? I looked into some calculations but most of them are needed for reference genes or some other stuff. The only thing that I have is cycle numbers and my primers' efficiency. Do you think I can do something with these inputs? (I know that cycle numbers mean nothing in a plot, so I do not want to put cycle numbers basically.)

Thank you for reading it. Any help/idea would be very appreciated. I am so desperate. Thank you.

OK, let us start from the beginning. We know what makes one cell type different from another cell type is its expression - i.e. what genes are actually being transcribed into RNA. Therefore, there should be certain RNA in one cell type that should not exit in another cell type. If you isolate RNA from a certain cell type, say a neuron and you want to show that your sample RNA contains only neuronal RNA, than you have to prove 2 things:

That your sample contains certain RNA sequences that are known to be in neurons
That your sample does NOT contain certain RNA sequences that are known NOT to be in neurons

There are several lab procedures for identifying the presence/absence of certain RNA sequences in a sample, your chosen technique is qPCR. Here is a brief explanation of how qPCR works.

You put your RNA sample along with a sequence specific primer in the qPCR machine. The primer will bind to a specific sequence and then that strand will be replicated. This will keep on repeating, cycle after cycle. So if you start with 1 sequence of say sequenceA, after cycle 1, you will end up with 2, then 4, then 8 and so on.

Anyways, if your goal is to use qPCR to prove your RNA sample comes from a neuron then you must find some sequences that are known to be specific to neurons. Then find primers for these sequences. Then use these primers to amplify some RNA from your sample. If you get amplification, then you must have had that sequence in your RNA sample. To further support yourself, you may also want to look up a few sequences that are known NOT to be expressed in neurons and using the same principle prove that these sequences are NOT in your sample.

The above will give you qualitative data, it will simply tell you if a certain sequence exits or does not exist in your RNA sample. Since you are only interested in the presence or absence of markers, this should be sufficient. Howver, if you would like to quantify your data, i.e. find out how much a certain sequence is expressed then read on.

You can also get quantitative data from qPCR (after all qPCR stands for quantitative PCR). The number of copies of an RNA sequence after a certain number of cycles is proportional to the initial number of copies of that sequence in your sample. In other words, if your initial RNA sample has a lot of sequenceA and a little sequenceB, then at any cycle, you should see more sequenceA.

We can take advantage of this relationship. There are two general methods you can use to quantify your results. One is called Absolute quantification and the other Relative quantification.

The idea behind absolute quantification is that you run two qPCRs. In one, you do your RNA sample. In the second, you run a standard sample, for which a standard curve is available. You can then compare your RNA sample results with the standard's results to get an idea of the number of copies in your sample.

The idea behind relative quantification is that you compare the qPCR results for your sequence of interest with the qPCR results of a refrence gene. This will only give you an idea of how many times more or less your sequence of interest if expressed than the reference gene. Since you do not have a refrence gene you cannot use this method, but you can use the absolute quantification method explained in the paragraph above!

Here are very useful links on quantifying using qPCR:
http://en.wikipedia.org/wiki/Real-time_polymerase_chain_reaction#Quantification_of_gene_expression

http://relative.gene-quantification.info/

Let me know if you need further clarifications.


How do genes determine facial features? What is known about the genes responsible for inherited facial features — the family resemblances that are so recognizable? Take for example a particular shape of nose: which gene or genes make it snub or Roman?

First, it's been estimated that the narrow-sense heritability of facial morphology is about ~60-90% (Martinez-Abadias et al 2009, Weinberg et al 2013, Liu et al 2012), so genetics is likely to be a greater influence than environment. But actually, the molecular genetic understanding of cranio-facial morphology is quite poor relative to other quantitative traits.
There's a list of genes from Wu et al (2019) which have been implicated and replicated across studies, but it's likely that there is a substantial amount of population specific differences in the effect size of different genes. The most replicable gene is PAX3 (which encodes a transcription factor).
As for the actual molecular genetics, it's complicated. Here are some quotes from a review (Weinberg et al 2018):

As with most common traits [61], the implicated variants from the
above facial GWAS tend to reside in noncoding (regulatory) regions of
the genome. Many variants at the 15 aforementioned facial loci were in or near
enhancers known to play a role in human craniofacial development.

An important finding from this study was that the effects of genetic
variants on facial morphology tend to be highly specific, even within
a single structural component like the nose. Another important finding
was that variants at these 15 loci tended to show preferential
activity in human cranial neural crest cells—a critical cell
population for building the face.

As for a more specific example, Adhikari et al (2016) peformed a GWAS on admixed Latin Americans and identified a significant association in the EDAR gene (well studied and known for being at high frequency in East Asian populations and influencing ear wax type, follicle/gland type and teeth formation). EDAR has a general role in the development of ectodermal tissues (such as the skin).
They found that the variant in EDAR was associated with reduced chin protrusion. Other studies have also shown that EDAR variants influence the cranial morphology in mice (using knockout studies). Functionally, they propose that:

The impact of the Eda pathway on mandibular morphology has been
interpreted as resulting from epithelial–mesenchymal interactions
during mouse craniofacial developme

References

Martinez-Abadias, N. et al. Heritability of human cranial dimensions: comparing the evolvability of different cranial regions. J. Anat. 214, 19–35 (2009).
Weinberg, S. M., Parsons, T. E., Marazita, M. L. & Maher, B. S. Heritability of face shape in twins: a preliminary study using 3D stereophotogrammetry and geometric morphometrics. Dent. 3000, 1 (2013).
Liu, F. et al. A genome-wide association study identifies five loci influencing facial morphology in Europeans. PLoS Genet. 8, e1002932 (2012).
Wu, W., Zhai, G., Xu, Z. et al. Whole-exome sequencing identified four loci influencing craniofacial morphology in northern Han Chinese. Hum Genet 138, 601–611 (2019). https://doi.org/10.1007/s00439-019-02008-6
Weinberg, Seth M., Robert Cornell, and Elizabeth J. Leslie. "Craniofacial genetics: Where have we been and where are we going?." (2018): e1007438.
Adhikari, Kaustubh, et al. "A genome-wide association scan implicates DCHS2, RUNX2, GLI3, PAX1 and EDAR in human facial variation." Nature communications 7.1 (2016): 1-11.


Why does caffeine consumption cause one to urinate more? What is the physiological mechanism behind the diuretic effect of caffeine?

Caffeine inhibits the secretion of the antidiuretic hormone (ADH), so it increases diuresis, but this effect is small and transient.
http://en.citizendium.org/wiki/Vasopressin

Caffeine in amounts up to 400 mg/day (~4 cups of coffee) does not results in net dehydration, since the amount of water lost due to slightly increased diuresis is much smaller than the amount of water in coffee.
http://www.ncbi.nlm.nih.gov/pubmed/19774754

In some people, caffeine may irritate the bladder and thus trigger more frequent urination, but this is not increased diuresis and the total volume of the urine is not increased.


What species is this bird (found in Cousset, Switzerland)? A friend of mine saw that bird in Cousset, Switzerland but it doesn't look like anything we know or we've already seen before around here. Does anyone have an idea of what species it could be? Thank you in advance (and sorry for the bad quality of the picture)!

This is really hard to tell given the quality of the picture. What size was it?

Could be Emberiza citrinella, the so-called yellowhammer - a year-long resident in Switzerland. It is about 16 cm in size and its breeding season starts beginning to mid-April and males are advertising for females in a golden plumage.

Again, this is only a best guess and without a better quality image it can never be more. RHA pointed out in the comments that the head of the bird in your image appears to be darker than one would expect in E. citrinella, suggesting it could also be E. melanocephala - the black-headed bunting, Spinus spinus - the Eurasian siskin, or Serinus serinus - the European serin. But consider this:

The bird on your picture appears to have a somewhat dark head but it does not seem to be black (but with the resolution it is hard to tell). E. citrinella males have brown stripes on their head that can be more or less pronounced (see examples in Google search for yellowhammer) - blurred, this fits the brown head in your picture.
In your comment, you give the bird's size as the size of a house sparrow which exactly fits E. citrinella.
E. melanocephala males have a pitch black head and the range it can be found does not fit your location. There are reports of vagrants but in combination with the brownish head in your picture this seems somewhat unlikely to me.
Sp. spinus and Se. serinus are smaller (max. of 12 cm in length) than what you describe.
Se. serinus is a partial migrant in Switzerland which decreases the probability of finding it in April, compared to a year-long resident. Additionally, it also only has brown stripes on its head.

In summary, I think the the most parsimonious call is that the bird on your picture is E. citrinella. However, keep in mind that it could also be one of the other species mentioned above, with E. melanocephala - given your size description and the dark head - perhaps being the second most likely identification.


Determination of a chemical compound in a non-homogeneous sample This is a more generalized question of my other question here.

I want to know if it is possible to determine a chemical compound in a non-homogeneous sample. I am asking this because we are aiming to create a device that will detect histamine level in fish without homogenizing the samples. In all the journals we've read (which are a lot), fish samples are homogenized (blended + chemically-treated) before histamine is determined.

I am a computer engineering student with basic knowledge on biochemistry. I'm researching on this because this is our thesis topic (which our adviser has forced recommended to us).

Any help/recommendation regarding this is appreciated. Thank you!

You should not actually homogenize samples because histamine works locally. If you know which region is releasing histamine then you can just study those regions. You can actually create a transgenic fish with GFP that is a target of histamine receptor signaling.

Using mathematical models or statistical correlations you can obtain the level of histamine based on fluorescence.

Activated histamine receptor H1 causes production of inositol triphosphate (IP3) which in turn causes release of calcium form ER. You can use Cameleon-GFP to sense the change in calcium levels. However, there are many events that may result in calcium release; you should carefully design your experiment.

This is another possibility (just a guess)- a FRET based study using GFP-YFP FRET Pairs (or other variants). Since histamine receptors are G-protein coupled receptors you may fuse the GFP to alpha subunit and YFP to beta subunit. When upon signaling, the subunits dissociate, you would see a decrease in FRET.


How common is complete heterochromia? How common is complete heterochromia? (One iris is a different color from the other)

Are there any statistics available for this? If no, why not?

Note: not my area of expertise

First of all, heterochromia can be congenital (found at birth) or acquired, and from your question it is not clear if you are asking about one specific type or the overall frequency (if so, at what age?). Since acquired heterochromia is often due to injury or disease, the overall frequency is likely to increase with age. Also see answers to the question "Is it biologically possible for an adult's eye color to change?" for more on reasons for acquired heterochromia.

According to an Austrian study (Stelzer, 1979), the overall frequency in the Vienna population was 0.26% (males: 0.16; females: 0.37). However, Medicine.net reports a frequency of 0.6% for only congenial heterochromia, but this number lacks a clear reference. A thorough review of different reasons for heterochomia can be found in Rennie (2012).


How do animals handle light refraction in different media? For a human, when diving underwater, everything is blurry because of the water's different refractive index compared to that of air, which we are accustomed to. How do animals, like turtles, seals or penguins, handle that difference when changing the medium? Are they nearly blind at surface and can focus underwater or the other way around? Can they adapt to different refractive indexes on the fly? How?

It is more complicated than this, but... I don't think it has as much to do with the refractive index of water but rather the shape of our corneas and the loss of this shape advantage under water, for if the eyes are protected by goggles, one can see quite clearly underwater (much the same as a camera can, as the shape of it's lenses are not affected). Any change in the shape of the cornea changes the way light passes through the eye, and results in a change in vision. The following is from Ch. 9 Optics of the eyes of marine animals, from Light and Life in the Sea:

This is different for penguins (and turtles): the surface of their eyes, the cornea, is not as much vaulted as for humans (it's much flatter), and the lens is much rounder (meaning the shape can change more than our relatively flat lenses can), so the difference between air and water is not so big and the light isn't refracted too strongly. Also, the ciliary muscles (not to be confused with the pupillary muscles) holding the eye's lens (behind the pupil) are stronger, increasing their accommodation, so a penguin has a sharp sight in the water. Or as stated in A Survey of Vertebrate Strategies for Vision in Air and Water

  Whereas the cornea is usually the major refractive element of the terrestrial eye, it is of little or no refractive consequence to an aquatic vertebrate.

See the difference in these four vertebrae groups (the first is man, the second is fish, the third is whales (similar to penguins) and the fourth is sirenians - manatees and dugongs)1:

Penguins.info
[1] Comparative anatomy and physiology of vision in aquatic tetrapods


Human defenses to toxoplasmosis Toxoplasmosis modifies the rat's brain to make them love (and be eaten by) cats. It also infects ~30% of humans, and modifies traits in several bad ways (i.e. schizophrenia and increased reaction time). However, humans are thought to be a "dead end" for the parasite. Thus, there is a significant selection pressure for humans to develop resistance but no (or almost no) pressure for toxoplasmosis to counter human resistance. If so, why are so many people infected?

Thus, there is a significant selection pressure for humans to develop resistance but no (or almost no) pressure for toxoplasmosis to counter human resistance.

Well, I think in this case "Significant" isn't qualified. Significant selective pressure can come in many forms, but as you mention about 30% of humans are infected with Toxopolasma, and the vast majority remain capable and functional. Remember that selective pressure applies to the ability to take advantage of resources and reproduce. People with toxoplasmosis are almost always capable of surviving and reproducing, so I doubt the pressure is all that much.

There is also significant incentive for Toxoplasma to develop the ability to adapt to humans, as it would open up a whole new resource for them to take advantage of. How fast the parasite is capable of adapting, or even if it's possible to eventually include humans in their life cycle, is something that would take some studying.

Our immune systems, in turn, try to kill the parasite regardless of whether we're being taken advantage of or not. You might be interested in reading up on the Red Queen Hypothesis - a theory that delineates how the immune system is at constant war with its environment and potential new threats.

As for your last question...

  ... why are so many people infected?

That's easy. :-)

Cats have become a popular pet, and most of the time the parasite doesn't significantly affect us. If either of those changes, you'll see a change in infection rates.


Wallace effect on human populations Could sympatric speciation occur in humans, for instance, separating blue collar workers from white collar workers?

No, it won't happen

Even geographical isolation failed to allow speciation in humans (see Does it make sense to classify all humans in a single species?). So if there is some small reproductive isolation between working groups, it is definitely not going to be strong enough to cause speciation.

In an imaginary world

If there was strong reproductive isolation

In an imaginary world where there is a more important reproductive isolation that lasts for long enough between blue and white collar workers, sympatric speciation might be possible. Such reproductive isolation could be caused by very important social stigmas.

Wallace effect

Wallace effect is a type of speciation that is mediated by a reproductive isolation that has been selected for as fitness of offspring is higher when mating is assortative.

There is probably relatively little genetic predisposition to being blue collar or white collar worker. But in an imaginary world where there is very strong genetic predisposition to being a good blue collar or white collar worker, and where worker quality will affect income which will affect fitness, then yes, wallace effect could be a thing.

But really, we do not live in one of this imaginary world. In our world, speciation won't occur between blue collar and white collar workers.


What role does a protein's size have on protein-protein interactions? Protein-protein interactions are when two or more proteins bind together, possibly for some important biological function.  Recently, I'm starting to look more into proteins, and in particular, networks related to proteins, such as protein-protein interaction networks.  I found myself thinking about the following question:

  Question:  Does the relative size of two proteins significantly affect how likely they are to interact?  Does it affect how they interact?

It would be plausible for me to download a protein-protein interaction network, and calculate their relative size from the proteins' PDB files.  However, I predict that the results from such a computation would not offer much insight into why (or why not) the protein sizes affect binding.

Protein interactions occur mostly (if not all) through residues that are on the "surface" and exposed to the milieu in which they exist, be it cytoplasmic or extracellular. So, a naive thought would be to guess that a greater surface area means a greater swathe of exposed regions and probable interacting parts. One protein can bind many others, even simultaneously, through different such interaction surfaces. However, other factors also determine whether a given set of two proteins interact, most important being where they localize in a given cell. If one protein is nuclear but the other on the plasma membrane, it is highly unlikely that they ever interact even if thermodynamics highly favors complex formation. Interaction between two proteins also depends on their respective conformations, which can further be regulated by events such as post translational modifications (eg., phosphorylation by a kinase), bound nucleotide state (eg., GTP vs GDP in a G protein). Last, scaffolds can also sequester and organize protein clusters together spatially and increase the probability of them interacting. All put together, I think it is highly unlikely that just looking at 3D surface area of a protein will say much about its "interactability" with other proteins.


MLE estimation with Mk model in ape or phangorn? When doing MLE with the R package ape or phangorn, is it possible to set the substitution model to Mk? If so, how does one do this?

From reading though the documentation, the Mk model does not appear available.

Although the JC69 model is, which this source describes as a slightly less generalized form as Mk.  The JC69 model still assumes equal substitution rates and equal base frequencies.  To use the JC69 model in phangorn set the model to "JC" and in ape set the model to "JC69".


Since frogs are ectotherms and supposed to have low metabolic rate, why do they grow so fast and eat so much? It's always emphasized in literature that endothermy enables high growth rates but requires more food.

But look at frogs, for example: bullfrogs, toads, pacman frogs etc. They would readily eat a quarter their weight a day, and they grow real fast (I used to keep pet frogs: pacmans, for example, become more that twice as big in one season). And all of that despite being ectotherms. How is that possible?

Rather than saying ectotherms can't grow fast (which is obviously false), it's probably better to think about it as a two-part argument:

Ectotherms and endotherms can grow rapidly at an optimum temperature
Ectotherms can't maintain themselves at their optimum growth temperature

If you keep ectotherms at their optimum temperature, then they can reach optimum growth. In the wild, they might not find that optimum temperature for more than a few hours per day, though in your aquarium they might be at it all day long.

There are several publications supporting this such as

Effects of temperature and volume of water on the growth and development of tadpoles of Pleurodema diplolister and Rhinella granulosa (Amphibia: Anura)
Effects of Temperature on Growth, Development and Survival in Larvae of Pelophylax ridibundus (Pallas, 1771) (Amphibia: Anura): Linking Global Warming to Amphibian Development
Thermal tolerance limits and effects of temperature on the growth and development of the green toad, Bufotes viridis

I don't see a specific reference for this but will add that ectotherm probably have greater growth potential than endotherms if they're at their optimum temperature, because endotherms have to waste energy on a whole suite of molecular machinery that's designed to maintain their body temperature.  All that extra energy can be diverted into growth by ectotherms.


What kind of insect is this? Found in Russia in the kitchen. It is about 3 mm long.

That is a flour beetle, the two most common and likely types are the confused flour beetle and red flour beetle but to identify look at the antennae. I'd suggest it is the confused flour beetle because the antenna go from thin to fat quite gradually, though the pictures may not be good enough for that to be certain.

Other commonly used names are tribolium (the genus name) or flour weevil. They are also used in labs as a model organism, groups in my last two labs have used them. They are a pest and you should probably get rid of them.

  "Both types of beetles are often found not only in infested grains,
  but in crevices in pantries and cabinet, as well. Damage to food is
  caused somewhat by the beetles' feeding, but also by their dead
  bodies, fecal pellets, and foul-smelling secretions. In addition to
  creating a foul odor, the beetles' presence encourages the growth of
  mold." - Wiki.


What limits our healing speed? Our bodies can repair quite a number of injuries very well. However, it takes time. For larger wounds, complete recovery can last many weeks. Why is this time so long, what is the most important limiting factor? The speed of cell division? I thought cell division was faster, and if necessary, cells could also be transported in the blood stream. Thrombocytes, as far as I know, are transported to the location of the emergency by the blood, and are not produced locally.

If the pure physics and chemistry allowed, for example, a 2x faster healing rate, wouldn't there be any evolutionary pressure for it?

The process of wound healing is pretty complicated and is much more than only cell division. The woundhealing process starts almost immediately in the moment of the injury and depending on the injury can take quite a long time. Have a look at the figure below (from the second reference), which shows the phases:

Basically this can roughly be diveded into four phases:

Hemostasis/Coagulation:

vascular constriction (blood vessel contraction)
platelet aggregation, degranulation, and fibrinformation (formation of a thrombus and closure of the wound)

Inflammation:

neutrophil infiltration
monocyte infiltration and differentiation into different kinds of macrophages
lymphocyte infiltration

Proliferation:

re-epithelialization
angiogenesis (formation of new blood vessels)
collagen synthesis (formation of new connective tissue)
formation of the extracellular matrix

Remodeling:

collagen remodeling
vascular maturation and regression

This process takes some time and can be prolonged when a wound is infected.  So I don't think there is much room to speed this up, as you need to go through all these phases. This process is also the result of extensive evolutionary processes; otherwise, such complex cooperation between different cells is not possible. For more details on the process itself, have a look at the references.

References

Factors affecting wound healing.
Cellular aspects of wound healing.


What is the biological/evolutionary advantage to baldness? Male pattern baldness is a common genetic trait. With a distinctive pattern/ density gradent (as apposed to general old age thinning as the body ages)

Hair has an advantage of protection from the sun/weather. So to lose it in a distinctive pattern (and lose that advantage) appears to have a reason*; and as it is a genetic trait, it seems like it would have been something that was selected for (or it would be more likely to be selected out).
So why is it better to develop pattern baldness as someone gets older?

So what might be the biological/evolutionary advantage to developing baldness?

Traits get selected for good and bad reasons(in retrospect), however I am interested in the reason why this particular trait has been selected.

* Lets assume that there is a specific cause (causes) and it is not just a leftover evolutionary artifact.

The related question: Why do some bad traits evolve, and good ones don't? provides some interesting background, but doesn't specifically address the What causes in this question.

Baldness would appear to be a trait on display. That being said, hair loss can be selected against the opposite condition (full head of hair), or selected by way of precise pattern deemed attractive. So, male pattern baldness evolution for mate selection purposes is probably a factor in play. But, either way, hair loss appears to have both its advantages and disadvantages as far as both fitness and mate selection is concerned.

Similarly, in terms of fitness, the advantage/disadvantage you state is the immediate positive advantage of hair as a protectant.  The immediate advantages of hair diminish as one grows older, making age apparent. Old age is disadvantageous in itself (older can mean less fit). Hence, the immediate advantage for a protection against the elements decreases and becomes less relevant to survival as one grows older. Please see the references below.

https://en.wikipedia.org/wiki/Mate_choice

https://en.wikipedia.org/wiki/Evolution_of_ageing


Is it possible to kill parasitic worms by intoxicating oneself? I've heard of parasites that can live in the human body and do a lot of damage to the host. There are even safer forms of worm-like parasites inside the intestine, but some parasites can live in the blood vessels or even in the brain or eyes.

Parasites are, in my opinion, the most disgusting creatures there are, so I wondered if they could be killed with intoxication.
Would it be possible to get rid of worm parasites in the blood by increasing the amount of alcohol in the blood to a level that humans can tolerate but parasites can't?
Could you also eliminate brain parasites with hangover-related brain dehydration?

That the dead parasites remain in the body may not be good or advisable. In addition, eggs, which are usually a little more resilient, should rather be removed from the body by antibiotics or proper medication. But is it at least theoretically possible to do something with alcohol against parasites?

In summary, there is no convincing evidence to say that alcohol intoxication helps to treat or prevent parasites in humans.

1) The evidence from in vivo human studies does not support the idea that alcohol consumption helps in treating parasites.

Alcoholism and Strongyloides stercoralis: Daily Ethanol Ingestion Has a Positive Correlation with the Frequency of Strongyloides Larvae in the Stools (PLoS, 2010):

  The frequency of Strongyloides was significantly higher in alcoholic
  patients than in control group (overall prevalence in alcoholic 20.5%
  versus 4.4% in control group; p = 0.001).

2) Even a strong alcohol beverage gets diluted when it reaches the intestine.

Ethanol concentrations in the human gastrointestinal tract after intake of alcoholic beverages (European Journal of Pharmaceutical Sciences, 2016):

  In a cross-over study, five fasting volunteers were asked to drink two
  standard consumptions of commercially available alcoholic beverages,
  including beer (Stella Artois®, 500 mL, 5.2% ethanol), wine (Blanc du
  Blanc®, 200 mL, 11% ethanol) and whisky (Gallantry Whisky®, 80 mL, 40%
  ethanol).

  The median gastric ethanol Cmax (min–max) for the beer, wine and
  whisky conditions amounts to 4.1% (3.1–4.1), 4.1% (2.6–7.3) and 11.4%
  (6.3–21.1), respectively...Median duodenal ethanol Cmax (min–max) for
  beer, wine and whisky are 1.97% (0.89–4.3), 2.39% (2.02–5.63) and
  5.94% (3.55–17.71), respectively.

So, the maximal ethanol concentration in the duodenum after drinking 80 mL of whisky was 17.7%. Most of ethanol is absorbed in the first part of the small intestine (Scandinavian Journal of Gastroenterology), so it does not reach the more distant parts and does not likely kill the parasites there.

3) Even strong intoxication is associated with low blood alcohol concentration.

In strong intoxication, your blood alcohol concentration would be only 0.2-0.3%. In one study (Table 1), the 50% lethal concentration (LC50) of ethanol, which killed 50% of the bloodstream forms of the parasites Trypanosoma brucei, was 10.6%.

4) Alcohol intoxication and brain dehydration

Alcohol intoxication or hangover are not automatically associated with dehydration. Anyway, even in severe dehydration, you still have a lot of water in your body, including the brain, so the parasites living there do not necessarily get dehydrated as a result of your dehydration.

In general, dehydration increases the risk of infections, because it dries mucous membranes, for example in the urinary tract (BMJ Open Quality, 2019).


Function of Smooth Muscles in the skin I understand that the overall function is voluntary movement, but is it the same in the skin? Is the main function in the skin movement or is there a greater function? Could anyone could provide this information or at least recommend a site that could help me with this research, as I have been searching and I haven't been able to find the answer?

Smooth muscle in the skin actually produces very little motion.  They are found in special places, such as the areolas of the nipple, the tunica dartos of the scrotum, and also around hair follicles.

Smooth muscles that surround hair follicles give you what is known as goosebumps - they contract all together, creating a bump in your skin around the hair follicle.  This can happen when you're cold, scared, or experiencing strong emotion.

Sources:

Skin Tissue Engineering and Regenerative Medicine, Justine Fenner, Richard A.F. Clark, 2016; Chapter 1


Understanding genetic similarity in humans I was reading "Blueprint" by Robert Plomin (online preview on webpage) and got stuck when I got to these two sentences in the prologue:

"We are the same as every other human being for more than 99 per cent of these 3 billion DNA steps, which is the blueprint for human nature." (page X)

"familiy members differ a lot genetically - you are 50 per cent similar genetically to your parents and siblings, but this means that you are also 50 per cent different." (page XI)

How does it fit together? Is he talking about different measures of similarity here?

Yes, these are different measures, and agreeably confusing. The "more than 99%" figure refers to pairwise distance. This figure (actually 99.9%) means that if you were to line up the 3 billion nucleotides of DNA from of any two people, on average, 1 in 1000 of these nucleotides would be different. Among siblings, this number would be even smaller. The 50% figure refers to the origin of DNA stands in a diploid organism: you get one exact copy of each of your genes from your mother, and an exact copy from your father. So half your DNA comes from each parent. But the DNA from each parent is still nearly identical. Siblings will get all their DNA from their parents, but for any particular section, they will get either their maternal grandmother's or grandfathers gene from their mother, and either their paternal grandfather's or grandmother's gene from their father.
For reference, you often hear that humans and chimps share 98% of our DNA. This is the not exactly a pairwise difference value, because it only counts changes in amino acids (http://humanorigins.si.edu/evidence/genetics). The amino acids between chimps and humans are about 98.8% identical to humans. The DNA across the whole genome is about 94% identical. There are about 50 genes present in humans that are absent in chimps https://www.genome.gov/15515096/2005-release-new-genome-comparison-finds-chimps-humans-very-similar-at-dna-level


What signals histone methyl transferases to function? I wanted to find out if anyone knows what stimulates histone methyltransferases to function?  I know that it is a process still trying to be understood, but I can't find anything that seems to direct the activity of the enzymes.  Additionally, where do the methyl groups come from that the enzymes transfer onto the histones?

Thanks!

Histone methylation is regulated by a variety of of events, including transcriptional activation and repression, relative location of the histone in the chromatin (pericentric or not, hetero- vs. euchromatin, etc.), X-inactivation, the cell's point in the cell cycle, and others. A variety of signaling pathways can lead to the (in)activation of HMTs. I found this table at cellsignal.com listing known methylation sites, along with literature references. Elsewhere on the site is this graphic, which shows some of the same info in a different way, and also has links to data at PhosphoSitePlus with links to the protein of interest. If you dig around, you can find all sorts of pathway and experimental information. For example, if you look up PRMT1 (human), you get a brief description of the protein and what pathways it's involved in, as well as links to all sorts of other info. On the histone side, a look at Histone H4 (human) allows you to look at individual modified residues (I picked K21-m2) and find all sorts of literature links and information about experiments used to determine its function.

PS: I'm not affiliated with Cell Signaling, I just think they have a ton of useful protein information, kind of like NEB for mol bio stuff...


Meaning of ‘NC number’ associated with a gene?‘ Genes in listings etc. often have a number of the type NC_000012.12 associated with them. How should this be interpreted?

This particular ID represent RefSeq accession number.
NC_ stands for a genomic molecule representing complete genomic molecule, usually reference assembly. Every sequence has a stable accession number, a version number, and an integer identifier (gi) assigned to it. RefSeq records can be distinguished from INSDC records by the inclusion of an underscore (“_”) at the third position of the accession number.


What is this creature? Where can it be found? I recently received the picture below from a friend and began to worry. Does it really exist? What type of creature is it? What habitat does t live in and what is its range?

The creature in the man's hand is a baby eel. Giveaways: it has fish eyes and the flattening of the tail. The lower right picture suggests it's a vertebrate (i.e. not a worm.)

Exactly which eel it is is unclear, but you can read more about it in the linked article. Indeed, your first picture appears in the article.

  These transparent wonders are not a species, but rather they are the second stage in the life cycle of a number of eel species in the family Anguillidae. This particular specimen is an American eel, Anguilla rostrata. For the rest of the post I'll focus on the life cycle of this species for simplicity's sake.


How to find idea for essay I'm studying microbiology in Iran
The university that I'm studying in doesn't provide that much help in research areas and we don't get to research or write essays that much ,while I'm trying to write an ISI essay and communicate with universities abroad in order to get admission for my masters degree and be able to study abroad
But the problem is , I don't know how to start and find ideas for writing papers and research
Like, what is the first step you take as a scientist when you want to start research?

You might want to start by browsing the research papers (think of them as "essays") at https://www.plos.org/ to find the areas you are most interested in.  They have thousands of peer-reviewed articles which you can read for ideas for your essay and research ideas.   You might then consider contacting the authors of those papers to inquire about education or work at their institutions.


Are there organisms with fewer than 1000 neurons? I'm developing neural networks comprised of just 3 to 10 layers of virtual neurons and I'm curious to know if there are any insect brains out there with fewer than a thousand neurons?

Are there any tiny creatures with small numbers of neurons?
Do neuronal maps exist for those simple nervous systems?

Short answer
As far as I know, a complete neural map (a connectome) is only available for the roundworm C. elegens, a nematode with only 302 neurons (fig. 1).

Fig. 1. C. elegans (left, size: ~1 mm) and connectome of C. elegans (right). sources: Utrecht University & Farber (2012)

Background
Looking at the least complex of animals will be your best bet and nematodes (roundworms) like Caenorhabditis elegans are definitely a good option. C. elegans has some 300 neurons. Below is a schematic of phyla in Fig.2.

You mention insects; these critters are much more complex than roundworms. The total number of neurons varies with each insect, but for comparison: one of the lesser complex insects like the fruit fly Drosophila already has around 100k neurons, while a regular honey bee has about one million (source: Bio Teaching).

Complexity of the organism is indeed an indicator of the number of neurons to be expected. Sponges, for instance (Fig. 1) have no neurons at all, so the least complex of animals won't help you. the next in line are the Cnidaria (Fig. 2). The Cnidaria include the jelly fish, and for example Hydra vulgaris has 5.6k neurons.

So why do jelly fish feature more neurons? Because size also matters. Hydra vulgaris can grow up 15 mm, while C. elegans grows only up to 1 mm. See the wikipedia page for an informative list of #neurons in a host of species.

A decent neuronal connectivity map (a connectome) only exists for C. elegans (Fig. 1) as far as I know, although other maps (Drosophila (Meinertzhagen, 2016) and human) are underway.

References
- Farber, Sci Am February 2012
- Meinertzhagen, J Neurogenet (2016); 30(2): 62-8

Fig. 2. Phyla within the kingdom of animalia. source: Southwest Tennessee University College


Why is there sperm mitochondrial suicide? The mitochondria in the sperm are digested upon entry into the egg, making mDNA inheritance exclusively female. What is the advantage of this? Wouldn't some male mDNA be beneficial because of the advantages of (at least a little) sexual reproduction?

Reference:
"Postfertilization autophagy of sperm organelles prevents paternal mitochondrial DNA transmission" (behind paywall, here's a ScienceDaily article discussing the results).

Edit:

Both answers seem valid but it is hard to quantify the relative costs.

Maternal inheritance of mitochondrial DNA is very well conserved, although some species, such as some mussels, show paternal inheritance.  As for why or what the advantage is, some of it is due to basic logistics: sperm cells have ~100-1000 mitochondria, egg cells have 105-106, so male contributions are largely washed out.  Plus, most mitochondria in sperm are toward the tail, which does not always or necessarily get inside the egg.

For a more selection-based mechanism of the actual destruction, think about what sperm do.  They are small packets of energy that do nothing but race until they die.  That's it.  Energy production, which occurs in the mitochondria, produces reactive oxygen that can damage genomes.  The mt-genome in the egg is far less likely to be damaged.

Additionally, I might look to chromosome uniformity.  Heteroplasmy does occur now and again, and it's not usually a good thing.  Mitochondria are very important, so it makes sense to have an all-or-nothing approach, lest any deleterious genomes persist.


How does the "heat vision" of some snakes work? Some snakes have an infrared sense which is used to track warmblooded animals.

How does that organ work? And would a similar organ be possible in a warmblooded animal?

Vipers, pythons and boas have holes on their faces called pit organs (Moon, 2011), which contain a membrane that can detect infrared radiation from warm bodies up to one meter away (Fig. 1). At night, the pit organs allow snakes to sense an image of their predator or prey (Source: Nature).

Fig. 1. Pit organs in python (top) and viper (bottom) as indicated by arrows. Source: Wikipedia

Nerve cells in the pit organ contain an ion channel called TRPA1, which detects infrared radiation as heat. The pit organ is part of the snake's somatosensory system, which detects touch, temperature and pain. It does not receive signals from the eyes. Hence, snakes sense infrared by detecting heat, not photons of light. Infrared radiation heats up the pit membrane tissue, and TRPA1 channels open when a threshold temperature is reached, allowing ions to flow into the nerve cells and triggering an electrical signal (Gracheva et al., 2010). Rattlesnake TRPA1 is activated by temperatures higher than about 28 °C — roughly the temperature a snake would 'feel' from a mouse or a squirrel about a meter away (Source: Nature).

Hence, this organ works best in cold environments where temperatures are low so that warmblooded prey stands out. Further, warmblooded animals won't be able to use this organ, as the pit would be ~37oC and not be able to detect anything below that temperature.

References
- Gracheva et al., Nature (2010); 464: 1006-11
- Moon, Anat Cell Biol (2011); 44(1): 8–13


Is returning cholesterol to the liver really performed by HDL? Various answers in biology SE, including two quite upvoted ones (1, 2) claim that (in humans) returning cholesterol to the liver is done by HDL.

If I understand correctly, Wikipedia's Reverse cholesterol transport page also says this is done by HDL.

However, this blog post (by Peter Attia) says:

  Historically this process of returning cholesterol to the liver was
  thought to be performed only by HDL’s and has been termed reverse
  cholesterol transport, or RCT [...]

  This RCT concept is outdated as we now know LDL’s actually perform the
  majority of RCT. While the HDL particle is a crucial part of the
  immensely complex RCT pathway, a not-so-well-known fact is that apoB
  lipoproteins (i.e., LDL’s and their brethren) carry most of the
  cholesterol back to the liver.  In other words, the “bad” lipoprotein,
  LDL, does more of the cleaning up (i.e., taking cholesterol back to
  the liver) than the “good” lipoprotein, HDL!

Which is right?

According to Reverse Cholesterol Transport: Molecular Mechanisms and the Non-medical Approach to Enhance HDL Cholesterol (Frontiers in Physiology, 2018), both HDL and LDL are involved in reverse cholesterol transport.

In short: HDL takes cholesterol from the blood (from lipid-laden macrophages) and delivers it to the liver 1) via scavenger receptors (SR-B1) or 2) via LDL and LDL receptors (LDL-R). (For a detailed explanation of the diagram, see the Figure 1. in the linked article. There's a similar diagram (Fig.1) in Journal of Cardiology.)

Petter Atti says in his blog (emphasis mine):

  Historically this process of returning cholesterol to the liver was
  thought to be performed only by HDL’s and has been termed reverse
  cholesterol transport, or RCT [...]

  This RCT concept is outdated as we now know LDL’s actually perform
  the majority of RCT. While the HDL particle is a crucial part of
  the immensely complex RCT pathway, a not-so-well-known fact is that
  apoB lipoproteins (i.e., LDL’s and their brethren) carry most of the
  cholesterol back to the liver. In other words, the “bad” lipoprotein,
  LDL, does more of the cleaning up (i.e., taking cholesterol back to
  the liver) than the “good” lipoprotein, HDL!

He says that LDL does "more of the cleaning" than HDL, which may be technically correct in the sense that more LDL than HDL particles may be involved, but this alone does not change the concept of good or bad cholesterol. In the image, you can see that the initial cleaning (step 2 and 3) is done only by HDL, so without HDL no cleaning might occur at all.

Low HDL and high LDL levels in the blood are known risk factors for atherosclerosis (NCBI Books, 2019). Not all LDL particles are bad, though, the most harmful are oxidized small dense LDL particles (Hindawi, 2017).


regarding genetic disorders related to protein production I am not completely familiar with biology, but i had a genetics course in college along with practicals. Forgive me if there is something wrong with my question.

Is there a genetic disease which results in partially functioning or complete non functioning of genes resulting in little or no production of protein for eg Muscular dystrophy.

so why can't we supply these protein from outside the way we do in the case of diabetes(insulin)?

There are many protein deficiency issues caused by genetic mutation for eg: Protein C whose deficiency causes abnormal blood clots. This protein is controlled by the PROC gene whose mutation causes Type I Protein C deficiency (reference).

There are treatments of replacing proteins like in the case of Protein C deficiency, protein C concentrates are used (reference). In the case of Alpha-1-antitrypsin (AAT) deficiency, augmentation is done with weekly intravenous infusion of the AAT protein (reference).

So in many cases protein is actually supplied from outside the body and also many protein deficiency conditions can actually be controlled with balanced diets (reference) which unfortunately is not a solution for insulin deficiency.


How can a plant become resistant to glufosinate? From Wikipedia, the mode of action of the non selective herbicide Glufosinate is:

  Phosphinothricin is an glutamine synthetase inhibitor that binds to the glutamate site. Glufosinate-treated plants die due to a buildup of ammonia and corresponding decrease in pH in the thylakoid lumen, leading to the uncoupling of photophosphorylation. The uncoupling of photophosphorylation causes the production of reactive oxygen species, lipid peroxidation, and membrane destruction.

Now, in this article from the University of California (Weed control, management, ecology, and minutia), it states:

  Researchers in Malaysia reported a few years ago on a population of goosegrass resistant to glufosinate in vegetable and orchard systems (Lee L J & Ngim J (2000). A first report of glyphosate-resistant goosegrass (Eleusine indica (L) Gaertn) in Malaysia. Pest Management Science, 56, 336-339).  For a number of years this was the only reported case of resistance to this herbicide.

What would have to happen in the weed for it to become resistant to this chemical/mode of action, and what would initiate this process?

Phosphinothricin is a metabolite from the bacteria Streptomyces viridochromogenes which has a protein called phosphinothricin N-acetyltransferase (PAT). This Protein inactivates the phosphinothricin which is the reason why S. viridochromogenes is not dying from it. If you want a plant to be resistant to phosphinothricin you can add the gen for the PAT protein to the plant genom.
This is also described in this paper about herbicide-tolerant crobs.

An explanation for the resistant goosegrass could be that somehow it got the gen for PAT, maybe by horizontal gen transfer from S. viridochromogenes.

In your case the publication which is cited in your source contains another possibility. "We hypothesize that reduced herbicide translocation is responsible for resistance to both glyphosate and glufosinate in these populations"


What type of white hard thing grows on lobster I have no idea how to explain it. It looks like mini white volcanoes growing on a lobster shell.  Is it bacteria or parasite?

These are barnacles, which are interestingly related to lobsters. See the image for comparision (from here):

They have a mobile larval stadium, but once they mature, they attach to a hard surface. They can be found on ships, surfaces in harbours, on whales and obviously on lobster shells. See here and here for some more details.


How to find out the when we had a common ancestor with a particular animal For example, Jordan Peterson claims that human and lobsters have a common ancestor X million year ago. I wonder, how does he know it?

I'd be so delighted to visit a website, where I could select two currently existing species and it'd show me how many years ago they had had a common ancestor. Does anything like this exist? Do we at least have a database, so I, as a web programmer, could create this kind of website?

TimeTree [http://www.timetree.org] is one site that allows you to look at times from divergence of various taxa. Their FAQ describes how they calculate the times by pointing to this paper: Tree of Life Reveals Clock-Like Speciation and Diversification, but in general they used standard molecular clock approaches. You ask about downloading their database: they say

  The TimeTree Database data is currently not available for download. Methods for making these data available in the future are currently under discussion.


Once food has been properly cooked is it absolutely safe? If you properly cook food (let's say in the oven for 2 hours) will there be no risk left? no pathogen will survive this?

No, no food is ever 100% safe, Prions for instance can survive anything short of incineration, spores can land on food in the transition from oven to wherever, some bacterial spore can survive high temprature, ect.


How is the protease inhibited by lopinavir different in SARS-CoV-2 compared to SARS-CoV? The protease inhibitor lopinavir, originally developed as a cure against AIDS and HIV, has been shown efficient against SARS Coronavirus SARS-CoV.

  Dayer M R, Taleb-Gassabi S, Dayer M S. Lopinavir; A Potent Drug against Coronavirus Infection: Insight from Molecular Docking Study, Arch Clin Infect Dis. 2017 ; 12(4):e13823. doi: 10.5812/archcid.13823.

Why is Lopinavir not efficient against SARS-CoV-2? Is there a difference in the gene encoding for the protease?

Is there a difference in the gene encoding for the protease?

This paper by Wu et al. annotates the SARS-CoV-2 genome and compares its divergence from other coronaviruses, which may help answer your second question.

This annotation includes 16 genes for non-structural protein ("nsp"). Supplemental materials for this paper indicate that all but two of these proteins (nsp7 and nsp13) have amino acid substitutions between SARS-CoV-2 ("2019-nCoV" in the paper) and SARS-CoV.

The gene nsp5 encodes 3CLpro (chymotrypsin-like cysteine protease), so there are differences there.

Literature suggests nsp5 and other non-structural proteins are potential targets for a number of antiviral therapies.

Another paper suggests further that lopinavir targets nsp3 products, among other proteins, in use against SARS-CoV:

  Lopinavir’s possible target is Nsp3b, Nsp3c, helicase, NRBD or E-channel with the mfScores of –158.050, –189.140, –114.018, –171.127, and –221.785, respectively.

The nsp3 gene contains a papain-like protease 2 (PL2pro) domain. Supplemental materials from the first linked paper suggest nsp3 has a different amino acid sequence between SARS-CoV and SARS-CoV-2.

It might be worth digging into the Wu et al. paper and the raw annotation data to look at what those a.a. substitutions are, to see if that might help in determining why lopinavir is not as efficient at inactivating PL2pro and reducing levels of the novel coronavirus.

It may also be worth considering the target itself. Going back to the Nature Biotechnology article:

  But Erik De Clercq, of the Rega Institute for Medical Research in Leuven, Belgium, says that in searching for or designing effective drugs against COVID-19: “We should stay away from antivirals known to be acting at targets not playing a role in the replication of coronaviruses.” Such drugs include penciclovir, which is targeted at the herpesvirus DNA polymerase, and lopinavir/ritonavir, which are targeted at the HIV protease. Instead, he would favor targeting a virus-specific protein such as the RNA-dependent RNA polymerase, noting that coronaviruses do not contain or use a reverse transcriptase.


Staphylococcus AG structure? I found this statement in my study materials in the section of Staphylococcus

  The AG structure:

  protein AG (species specific);
  polysaccharide AG (serotype specific).

I know what is Protein A/G, a recombinant fusion protein that combines IgG binding domains of both Protein A and Protein G.

What is the point of this AG structure thing in the contex of Staphylococcus?
Can we say that staphylococcus have AG structure?
I think it has properties related to protein A\G and also to polysaccharide A\G.
I know very little about polysaccharide A\G and not sure how it is related to serotype specificity in the context of staphylococcus.

Extension to the question

Antigenic structure of Steptococcus pyogenes:
the group AG is unique, placing streptococcus in group A.

What is the AG here?

After puzzling over this for a while I think I have the answer . It's nothing to do with protein A or protein G. I think that whoever wrote your study materials meant Ag which is a common abbreviation for 'antigen'. I guess this was in the context of immune responses, or strain typing.

Looking back over your last few questions, it seems that you are at the mercy of a teacher who specialises in ambiguity.


Why babies cry after they are born? Well I have noticed that almost all of the babies cry after birth, but some of them (1 to 1,000,000? births) don't cry. So, we have:

Why is this happening (the cry after birth)?
Also why animals babies don't cry when they are born, but human babies cry? I have noticed that many mammals such as giraffes or chimps don't cry at all (The chimp only makes it's ordinary sounds).
Are there any special genes that humans have and animals not?

I'm answering this question (mostly) based on prior knowledge.

Inside the womb, the foetus relies on the mother for oxygen i.e. it receives oxygen from the mother's bloodstream via the umbilical cord.  A foetus doesn't use its lungs for breathing inside the womb. Ever.

Besides, lungs of a foetus are considered fully matured no earlier than the 36th week of pregnancy. (Though there are exceptions to this)

  During fetal life the baby's lungs are filled with fluid and they do not perform any respiratory functions. [1]

At birth, the baby is forced to breath on its own for the first time. Hence, the baby cries - or more precisely - gasps for air.
This 'cry' of the baby is actually a strong respiratory effort, thereby aiding the baby in its first breath. This is also why newborns don't produce tears on their first cry. Because it's not really a cry, it's a gasp for air.

Now the reason why such a considerable effort is required for the newborn to breathe is because:

A) Lungs are being used for the first time, and

B) The lungs of a foetus are filled with amniotic fluid when it's inside the womb. Effort is needed to push this fluid out from the lungs after birth.

I'm not aware if there's any genetics involved in this. I don't think there is.

Source: [1] http://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/babys-first-cry/article2267767.ece


Why do my muscles move slowly when cold? When my hands are cold, e.g. outside in the winter with no gloves for a while, their muscles begin to move slowly (assume I'm otherwise comfortably warm, e.g. dressed well but gloveless).

I don't seem to lose strength or endurance really, only maximum speed. Coordination is difficult and rapid repetitive movements are impossible, attempts instead lead to a continuous contraction (like normal, but the threshold is much slower). Of course normal function returns when the temperature is brought back to normal.

Why is this so? What is the correlation between lower temperatures and slower muscle response? Is it something with the neurons, something with the muscle tissue, or both? Is it related to blood flow (like when my hand "falls asleep" when circulation is cut off) or is it a property of the tissues themselves?

Sorry for the delay, I was low on time and didn't want to post a poor answer. Let's get into it step by step. The most important thing here is to understand that every single thing you do is a combination of many highly complicated biochemical and biophysical reactions/processes that slow down as temperature gets lower. Since any chemical reaction is a physical process I won't differentiate physics and chemistry any further. The speed of molecular processes is explained by thermodynamics. And in thermodynamics, all other things being equal, things slow down as the temperature gets lower, because temperature is a measure of thermal motion. Why? We will get to that later.

Now, what are those processes we are talking about? I'm not going to list every single molecular cascade in a eukaryotic cell that has something to do with muscle contraction (there are many, believe me). Instead, I'll give you a beautiful example that is directly related to movement. That is innervation. Everyone knows that neurones use axons for long-range transfer of electric impulses. Although people tend to portrait axons as wires, they really are nothing like metal wires, because the resistance is so high any biologically feasible electric signal won't travel for long. So how do axons work? Let's look at one:

Imagine a chain of Wi-Fi base-stations that retransmit a signal and you have a very good analogy. Any axon is mostly covered by glial cells, forming an isolation-coating (myelin sheath), but there are regular coating-free patches (Ranvier nodes). These nodes are the "base-stations". When a neurone sends a signal, it triggers the depolarisation of its cellular membrane by opening various ion-channels. The first Ranvier node senses the change in the electric potential and opens its own potential-sensitive ion channels, so the signal travels from node to node. In order the neurone to transmit a signal again, it has to recharge all the nodes (obviously, it takes time). The process is done by special active ion-pumps that use energy (ATP) to move ions against the concentration gradient. Now, let's list some thermodynamic processes:

Something senses the change in electric potential and changes its conformation. This is work.
The movement of ions along the concentration gradient. This is diffusion.
Something senses that the membrane is depolarised and triggers recharging. Once again, work.
The movement of ions against the gradient. This is done by molecular machines that require ATP. So here we have at least 2 reactions: 1. an ATPase transforms ATP to ADP; 2. an ion-pump works. Hey, what is work after all? ;)

In fact, a similar list of processes can be given for the actin-myosin system that actually performs the muscle contraction, when the cytoplasmic concentration of Ca ions increases after they are set loose from the intracellular Ca-storage facilities (the reticulum) in response to a neuronal or mechanical signal. It's just another charge-shoot-sharge cycle.

Now let's return to thermodynamics. First, consider diffusion. Diffusion depends on the speed of the molecules. The speed depends on temperature. So this is clear and simple (if you don't want to know, why it does). Now, let's consider reactions. Any reaction/process is probabilistic. We call reactions "fast" when the probability is so high there is no lag between individual events. Where does that probability come from? Although details, such as free energy distribution model (e.g. Maxwell distribution in ideal gases), depend on the medium you analyse, the basic idea of any reaction is to reduce the potential of a system. Aside from concentrations, there are 3 basic things to consider: 1. the starting free energy, 2. the activation energy, and 3. the resulting free energy. Let's look at a picture.

The higher the difference between 1 and 3, and the lesser the difference between 1 and 2, the higher the probability. Okay, this doesn't completely explain why this stuff is probabilistic. The thing is that the starting free energy of reagents forms a distribution, hence only a fraction of molecules have the energy to break the activation barrier. Any time two molecules (that could possibly react) meet, you play a game called "can we make the jump or not". The game is clearly probabilistic. When you lower the temperature, you shift that distribution, reducing the fraction of molecules that can make the jump.
Now we can go further into details, but I feel like this is already enough to give a sense of why things slow down as you lower the temperature.


Practical Question about Evolution, Population Genetics and Speciation North American cicada male of the genus Magicicada sing depending on the species at different times of the day and attract the females of the corresponding species. The species are very similar, but when crossing they have sterile (infertile) offspring.

In the species M. tredecim the time of the song is determined by the gene locus EARLYBIRD in an intermediate inheritance: The allele EARLYBIRD leads in the homozygous state to morning singing, the allele earlybird leads in the homozygous state to evening singing, heterozygotes sing at noon.

How does the frequency of the earlybird allele in the species M. tredecim change when the number of females of M. tredecassini increases? Does it increase, decrease, or does it remain the same?

I think it would not change the frequency of the earlybird allele, because they don't have a evolutionary advantage. But maybe it could also decrease the frequency, because infertile descendants sounds like a disadvantage? But I'm totally not sure and can't provide a real 'biological' reason since my thoughts are more like intuition.

Infertile descendants indeed sound like a disadvantage. Individual must invest a fair amount of resources into making an offspring. Making sterile offspring is just a waste of resources as those offspring aren't going to pass on any gene further to any grandchildren.

If there is an increase of the tredecdssini females, then male tredecim that sing quite late are going to mate with many tredecdssini leading to the production of sterile offspring. There is therefore selection against the allele 'earlybird' leading to an increase in frequency of the 'EARLYBIRD' allele.


Inheritance of mitochondria Imagine an isolated population in which each adult female has a distinct mitochondrial genome. In each generation, every adult female has two children (with a 50% chance of being male or female). After each generation, we will assume that all the adults die out, and all the children become adults.

After four generations, what is the expected percentage of mitochondria from the original population of females that will still exist in the population’s children? Express your answer as a decimal between 0 and 1, rounded to three decimal places.

Note: after one generation, there will be 100% of the mitochondria from the original population present in the population’s children since male children receive the mitochondria from their mothers (but do not pass them on to their own children.)

This is a question that is not as straightforward as it may seem.

One could make arguments, some better than others perhaps, for several different answers. The way it is worded, one could defend answers from 0.000 and 1.000 and many of the intermediate numbers as well.

  After four generations, what is the expected percentage of mitochondria from the original population of females that will still exist in the population’s children?

0.000; the original women died; THEIR mitochondria died as well. None of the original mitochondria still exist.

That may seem, and it largely is, a matter of semantics, but in some ways, it is true without word games.  Every time the mitochondria split, the copies are not EXACTLY the same.  The changes may be so minute they are not always detectable with the current technology, but that does not mean they do not exist.

Some changes occur to the underlying genome; they are rare and may not be readily observed, but that does not mean they do not exist as well. When one of these changes occur, all subsequent mitochondria will have the new genome assuming, of course, that the genome is viable.

If the change will not allow the cell to function properly, this will undoubtedly affect whether the child, as a whole organism, is able to survive.  Depending on the severity of the malfunction that results from the new genome, it may make it more difficult, perhaps impossible, for the offspring to thrive, to mate, and to produce their own offspring which can accomplish the same.

It is also likely that some of these genetic mutations will result in change that is too minute to have an effect on the mitochondria or how it functions. By the same token, it is likely that eventually there will be a mutation in the mitochondrial genome that will have a marked effect on cell function. The change may even improve the overall function of the organism to an extent that will enable the offspring to thrive, to mate, and to produce their own offspring at a greater rate than organisms that do not have this change. Needless to say, the 'improved offspring' will pass on their 'improved genome' to the lucky offspring that will be more likely to thrive and pass it on to the next ..... etc.

There are many factors influencing how well the new genome is going to spread. The population in this particular question was somewhat isolated; this will encourage the genomic change to spread through the general population more quickly. The rate of the spread, however, is affected by many variables.

So in a world with no mutations or any other factors that can result in changed mitochondrial DNA, it would be 1.000 as every offspring gets its mothers, who got it from hers, who got it from hers, so the four types, on an isolated island, would remain four types.

However, in reality, changes do happen. An error(s) in transcription would be one of the most common, but certainly not the only, process that could result in any DNA being changed in a heritable manner.

There is an average rate of mutations. In fact, one can look at the mitochondrial DNA of two individuals and calculate how long ago the genomes were essentially the same. In other words, one could look at a mitochondrial genome from some ancient fossil and tell how many generations it likely took for it to evolve in to the genome of a particular modern individual.  However, as these changes start as mistakes, it can take several generations for a change that is adaptive and will spread to occur.

The only way humans can observe these changes are in animals with very short life spans, such as fruit flies.

There would be very little change likely in only four generations; therefore, unless you had a very large sample size, any prediction would have little more than a theoretical chance to be correct.


Why do bananas grow curved? This old common question is still not clear to me. I got this explanation:

Bananas go through a unique process known as negative geotropism. Instead of continuing to grow towards the ground, they start to turn towards the sun. The fruit grows against gravity, giving the banana its familiar curved shape.
But why? The answer lies in the botanical history of the banana. It originated in the middle layer of the rainforest, where there is little sunlight. If the fruit were to grow towards the small amount of light that penetrates sideways through the vegetation, the plant could overbalance and topple over.
So bananas developed a way of growing towards the light without destabilising the plant.

source
So, evolutionarily, the bananas are 'forced' to grow towards the light. But how is this capabilty 'grown into' the banana? Is it something epigenetic or is it just light that attracts them? So how does this mechanism works?

The "proximate cause" would be a differential rate of growth on the different sides of the individual bananas. If the cells on the underside of the banana are dividing faster than those on the top, that will cause the upward curvature.

As to what causes the differential growth: I'm not a banana biologist, but I would suspect that a growth hormone of some sort finds itself more highly expressed in the part of the fruit that starts out closest to the stem.

Why that hormone might have decided to start doing that, and what selective advantage it might have given the early wild bananas, I have no idea. But our modern cultivated bananas have probably been strongly encouraged to do it, for compactness of shipping, if nothing else!


How does energy conversion happen (chemical to mechanical?) in moving body muscles? From my understanding, the brain sends electrical pulses through neurons to different part of the body to initiate a movement. My question is, how is the movement realized? For example, in a train, steam engine is used to convert heat energy to mechanical energy to move the engine. Similarly, in the body, I understand the energy is stored in chemical form. How is this converted to the mechanical motion of a body part?

The conversion from chemical to mechanical energy is in general done by molecular motors which perform a power-stroke, using the hydrolysis of adenosine triphosphate (ATP) or more rarely of GTP to power a change of their conformation while bound to cytoskeletal elements.

Molecular motors include myosins, which is the molecular family powering muscles in interaction with actin filaments but also other cells e.g. for their motility or for morphogenesis. animation  of muscle contraction

There are also kinesins and dyneins, not used for muscle function, but which perform e.g. transport of "cargo" organelles along microtubules.

An alternative way to produce mechanical energy is via ion pumps, as is the case in flagellar rotors.


What factors affect the number of individuals in an animal group? Social animals can live in groups whose numbers vary greatly according to species (for instance wolves vs deer herds vs buffalo stampedes vs lemmings).

Is this number regulated only by environmental factors (resource abundance, position in the food web etc) or is there a genetic upper bound to this number which prevents overcrowding? Put in other words, would a species with endless food resources (but finite space) grow endlessly?

If the genetic regulation is common, then why humans don't seem to be subject to it?

this depends on what you mean by group.

If you mean population then it is mostly environmental factors, although part of the environment can be other member of your species, some groups have a minimum functional size, such as passenger pigeons and breeding in groups behavior, or have density controls(if you are too spread out you might never run into another member of your species to breed with) , these internal factors are fairly rare however compared to basic resources availability, things like food, water, territory, shelter, nutrients, ect.

If you mean size of individual packs, herds, ect, then it is a mix of both, behavior which is almost always genetic is the main cause. However this behavior can be alter or triggered by environmental factors and its ultimate evolution is strongly affected by those factors as well. for instance large herd behavior will never evolve if the environment cannot support it, and if the environment changes the behavior may stop being beneficial.


Why is the penicillin/ceftriaxone hypersensitivity test only done once? I have had a severe bacterial infection. I was prescribed ceftriaxone, and when the time came for injecting it the nurse asked me whether I have an allergy to ceftriaxone. I answered that it's my first time, so she did the test and it was negative.

I was expecting a second test because as far as I know from type 1 hypersensitivity the body -  even if it is sensitive to an allergen - won't show a reaction the first time. The body makes the particular IgE and in the next exposure of same allergen it will have an allergic reaction.

So why is only one test done, considering the first two columns of the following picture?

From: Harsh Mohan's Pathology textbook 7E

Because developing a hypersensitivity takes time. If you get exposed to an allergen, the body first has to produce those antibodies that then get used in the hypersensitivity response at the second, or subsequent, exposure.

If you are talking about taking a second test just minutes after the first one, how would your body even "know" that this is a second exposure? Two exposures within minutes are not distinguishable from one exposure for the body.

Usually, an allergic reaction shows the second time a patient takes a full course of antibiotics. It does not show at the second oral dose or injection, which are way too close to the first dose to have already lead to the developing of a hypersensitivity.

So, why test you in the first place? Because you might have been exposed previously without remembering it - people misremember what medication they got during their childhood all the time, I imagine, and your doctor/nurse seem to just routinely do the test before giving these antibiotics.

Sources/Reading

Drug allergies

Update on the Management of Antibiotic Allergy