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The shape of the pupil depends on lifestyle
August 24, 2015 Newsadmin
Fig. 1. A – form pupil: vertical (cat), rounded (lynx), round (men) and horizontal (sheep). B – distribution of 214 species of animals in the form of the pupil and lifestyle (Herbivorous – herbivores, Active – active predators, searching for prey, and Ambush – predators lying in wait to ambush the victim). Drawing from the discussed article in Science Advances
In terrestrial predators attacking from ambush, most common vertical slit pupils, while their victims, herbivores, slit pupil often oriented horizontally. Scientists explain this pattern different purposes of the two groups of animals. Vertical pupil allows predators to see sharper vertically oriented objects, such as their victim, herbivore, on the contrary, it is necessary to survey the wide horizons in time to notice a predator, so their pupils are often adapted to ensure that the horizontal lines are sharply visible.
The pupil regulates the amount of light falling on the retina. In addition to the round pupils, the lumen of which is determined by the circular muscles – sphincter of the pupil, in the nature of frequent slit-shaped pupils are provided with an additional pair of muscles. The range of the slot-like clearance pupil wider than that of a round: the area of the vertical pupil cat can vary 135 times, and the round pupil person – only 15. Therefore, slit pupils useful for animals that are active during the day and at night, a wide range of lighting conditions. After all, the day when the light, the pupil should not miss too much light, and at night it is, on the contrary, should be as wide as possible to the retina fell out, and more so the small number of photons.
But the gap pupil can be oriented in different ways – vertically or horizontally. Scientists from Durham University and California have recently suggested that the orientation of the pupil is not random and depends on the lifestyle of the animal, and the objects in the visual field, which is especially important for him. They compared the shape data 214 pupils terrestrial species to their way of life (Fig. 1). It turned out that the pupils herbivores are mainly oriented horizontally in active predators most common round shape of the pupil, and the predators that lie in wait to ambush the victims, most of the pupils are oriented vertically. The shape of the pupil and depend on the period of daily activity: nocturnal animals often pupils were slotted than round. Regularities found corresponded very stringent levels of significance, so had to understand what the reasons explained by the difference in the shapes of pupils of different groups of animals.
Fig. 2. The depth of field vertical pupil
Fig. 2. Vertical pupil allows the animal to sharply enough to see the vertical contours, located a little closer or farther focal distance. However, horizontal lines, even a little bit far from the focal distance, look much blurred. If the pupil is horizontal, the picture will be the opposite. Drawing from the discussed article in Science Advances
When the eye or the camera focuses on a certain point, the rest of the image becomes blurred. The diameter of the blur circle around a specific point of the visual field depends on the difference between the distance to it and to the point on which the eye is focused, and the diameter of the pupil. If the pupil is not round, the cutting depth of the visible space will be different for different directions. For example, an animal with a vertical pupil will sharply enough to see not only the vertical line on which it is focused, but also vertical lines located farther or nearer the focal length. But to the horizontal contours of a pupil adapted worse and horizontal lines on which the animal itself is not focused will be very blurred (Fig. 2). In animals with a horizontally-oriented slit-shaped pupils is the opposite: they see a sharp horizontal contours, and to perceive vertical objects adapted not so good.
Fig. 2. Vertical pupil allows the animal enough to clearly see the vertical contours, located a little closer or farther focal distance. However, horizontal lines, even a little bit far from the focal distance, look much blurred. If the pupil is horizontal, the picture will be the opposite. Drawing from the discussed article in Science Advances
The benefit of a particular form of the pupil depends on the height at which the animal's eyes are placed. It is easy to understand, considering the photos taken with different distances from the subject, the closer to the surface of the camera is, the higher the gradient blur that is not in focus (Fig. 3). Therefore, if we compare, for example, a cat and a man, the cat is much more important to correct motion blur, because it is "closer to the ground" than people. For these reasons, scientists have suggested that animals smaller growth slit pupils are more common, and this hypothesis was confirmed when researchers analyzed data on the size of the animals from their sample. Interestingly, birds pupils almost always round, with one exception – at the skimmer vertical slit pupils. This exclusion is suitable for theoretical calculations of researchers because of lifestyle skimmer reminds terrestrial predator of small stature. This bird is flying very low at the surface of the water, preying on fish, so that all concerns about the vagueness of the image on which the face at close range, hold for skimmer.
Fig. 3. Simulated view of a plane for animals of different heights (0.6, 0.2 and 0.1 m). Left greatest height, the right – the smallest. The closer to the ground located the eye of the animal, the more blurred look objects do not fall into focus. Drawing from the discussed article in Science Advances
Why the eyes of predators attacking from ambush, better able to see the vertical line, and their eyes herbivorous victims, on the contrary, are set to horizontal contours? One can only assume that the predator is more important to see the victim (which is more like a vertically oriented object), and the victim, on the contrary, it is necessary to survey the wide horizons, which must be clearly visible to her in time to notice the threat. In addition, the victim need to determine the direction of where to go, and you need only predator chasing the victim, and the surrounding open spaces is not very interested.
Various forms of the pupil several times independently during evolution occurred. It turns out that some form of pupil in animals with different ways of life – this is an example of convergent evolution, when the useful life sign parallel develops in organisms other than the closest groups.
Kids Games accelerate the development of motor skills at the cost of slowing growth
Fig. 1. In addition to accelerating the development of motor skills in Assamese macaques games can provide other advantages – for example, to train the communication skills or the ability to make quick decisions in unexpected situations. Image source planetstillalive.com
The more time a young Assamese macaques spend on the games, the more quickly develop their motor skills, but the slower they grow. These observations suggest that the animals can spend time playing, even if it will have to sacrifice for the sake of the resources needed for growth. This behavior could be fixed only if the benefits of skills development that helps the game is very high.
During games, spend time not only people, but also many animals – primates, felines, dolphins, crows, small rodents. It is believed that playing only those animals that have enough resources to more utilitarian needs – nutrition, growth, protection of the territory. However, new data from the German naturalist, said that playing in some animals may be located closer to the base of the pyramid of values. Young mountain monkeys, or Assamese macaques, for example, often prefer to save on growth and spending power in the game. This distribution of scarce resources may be justified, because the game speed up the development of motor skills in these monkeys.
Although it is often said that the games help develop motor skills, this idea has not yet been accurately proven. Only circumstantial evidence was – for example, the coincidence of the peaks with the peaks of the gaming activity synapse formation in the motor cortex in several animal species. And if we talk about examples of animals that have long played and in which motor skills are well developed, the cause and effect here can be swapped – no motor skills are developed through games and play more than those who have the ability. To distinguish between these two options, it is necessary to observe the animals with his early childhood. Then you can learn and how to develop his skills, and how they can be associated with a love of games.
Such observation of cubs Assamese macaques in the wild habitats conducted by German researchers from the University of Göttingen Georg-August for two years. Scientists interested in not only the potential benefits of the games, but also their "cost" for the animals. Game – it is an activity that brings tangible benefits here and now, so that in a first approximation, it can be regarded simply as a waste of energy.
The researchers wanted to test whether the animals to play not only in the "fed" the times when there is enough food. Therefore, in the vicinity of the habitat study group monkeys are evaluated further and the number of fruits, which are eaten by monkeys. And in order to determine whether the growth of young macaques waste of effort to the game, the researchers several times a month were evaluated for their size photos. All study was delivered in a way that researchers have minimal impact on the natural way of living apes and just follow the life of animals from the side.
Scientists have recorded in detail how to spend time 17 young Assamese macaques. He was important to estimate the proportion of time that each of the young dedicates games, and find out exactly what is the game – single or group, with objects or locomotor (catch-up, or a pile-small) – and how these games are active (running whether participants go or sit on the ground). This latter aspect was important to assess to account for differences in energy costs on different types of games. To assess the potential benefits of the games, the researchers identified 17 motor skills (such as running or jumping from branch to branch) and recorded when one of the young for the first time applied a particular skill. It was assumed that the game may affect how quickly young macaques will acquire motor skills.
The study proved that the growth rate is inversely proportional to young rhesus time which they spent in active games (Fig. 2). The largest proportion of time spent in games – 12.2% – in line with slower growth at 30%. To play longer, animals refused not the search for and consumption of food, and from the rest. Therefore, a delay in the growth can not be attributed to a lack of supply of those animals who are too addicted to games; growth slowed down because of the expenditure of energy on the game itself.
Fig. 2. Linkage growth rate (vertical axis) and the percentage of time spent in games (horizontal axis). Data is given as a percentage deviation from the mean. Fig. discussion of the article in Science Advances
The more time young macaques were performed and playing games were more active, the faster they develop new motor skills. And because the skills that researchers have identified, appeared in the animals after they started to play, it can be concluded that it is active games caused the accelerated development of the skills of those who have played a lot, and not vice versa.
Young males performed in games longer than the female, and as a result, motor skills develop faster than males. At the same time, behind males from females in growth, reaching adult body size an average of five months later. The representatives of the Old World monkey family, to which the studied species of monkeys, females can not invest so much in the game forces the males, as the rate of growth and maturation of females depends their reproductive success. For males this relationship is not the same, so they can afford to invest in the rapid development of motor skills. It can help the male to take a privileged position in the community and eventually affect his fertility.
It is interesting that Young did not stop playing, even in difficult times, when the fruit was scarce, although lack of food further slowed their growth. It turns out that the game among young macaques – important article of energy costs and that the animals do not play only when they have enough resources. And when all the power is not enough, even the animals sacrificed growth rate for the game. This behavior could be fixed only if the game in the end turn out to be beneficial for the animals. In addition to accelerating the development of motor skills, which is especially important for males Old World monkey, games can provide other advantages – for example, to train the communication skills or the ability to make quick decisions in unexpected situations. Interestingly, these skills may be more important than the rate of growth not only in humans but also in Old World monkey monkeys.
Childhood primates very long. Often write that it is necessary for the development of the brain and the acquisition of complex skills, but until now it was not clear why these processes should be associated with such a slow growth. Recent data suggest a mechanism that can bind develop important skills at the speed of growth: through games – expensive but great fun.
Analogs contemporary moles, otters and primates existed in the Jurassic period
Fig. 1. Three Jurassic animal – like a squirrel, tree shrews or lemur Agilodocodon, digging krotopodobny Docofossor and waterfowl, like an otter or beaver Castorocauda – demonstrate the diversity of morphology and ways of life of early mammals. Drawing one of the authors of one of the items discussed, April Isch Neander from the University of Chicago, from a site sci-news.com
Fossil remains of two primitive mammals found in the mid- and late Jurassic deposits of northeastern China, showed that the Jurassic beasts were more diverse than previously thought. One of the new species led a burrowing lifestyle and remotely resembled a mole; the second lived in the trees and looked like a modern squirrel or tree shrews. Both species belong to dokodontam – a dead-end branch of the basal mammals consisting in a more distant relationship with placental and marsupial than the platypus and echidna. Apparently, many adaptations, such as the reduction of the lumbar ribs, and phalanges have evolved independently in the different groups of mammals based on the same genetic mechanisms.
It was once thought that almost all Mesozoic mammals were small, inconspicuous and monotonous, like shrews. However, the findings of the last decades, many of which were made in China, denied this view. "Elements" talked about some of these discoveries, including the amazing waterfowl "bobrohvoste» Castorocauda from the group dokodontov (Docodonta), which resembled an otter Borba and both could eat fish (see ref. At the end of the news).
Chinese and American paleontologists reported in the latest issue of the journal Science just two remarkable finds made in the north-east of China. The findings showed that the ecological and morphological diversity of Jurassic mammals were even higher than previously thought.
Both new kind as mentioned above bobrohvost refer to dokodontam. This group, according to many experts, is one of the deadlock (who left no living descendants) basal branches, separated from the common trunk mammal before, the latter divided into the ancestors of modern monotremes (platypus, echidna) and terievyh (marsupials and placental) . However, there are others, including radically different versions of the classification of mammals and their ancestors (see .: MF Ivakhnenko. The problem of transition Theromorpha – Mammalia).
The first of two newly discovered animals called Docofossor brachydactylus, meaning "digging shirokopaly dokodont." His bones were found in Late Jurassic deposits, Hebei Province (Fig. 2).
Fig. 2. Docofossor brachydactylus: general view of the findings (A), the portrayal of what remains of the skull (B), and the reconstruction of the skeleton (S). The image of the article under discussion Zhe-Xi Luo et al. in Science
Dokofossor – mammal a length of about 9 cm (from nose to base of tail) and weighing 13-17 In the structure of the skull and teeth are, on the one hand, primitive features characteristic of other mammalian basal (mammaliaform, mammaliaformes), on the other – specific features characteristic of modern burrowing animals such as marsupial moles and golden mole. The most convincing evidence in favor of digging lifestyle revealed in the structure of the limbs. Paws dokofossora – a specialized foot underground dweller. In particular, his fingers are made up of only two phalanges (instead of three, as in most ancient and modern mammals), and the terminal phalanx enlarged, expanded like a shovel, and a special projection at the base prevents the terminal phalanges folded back. All this – typical signs of burrowing animals. For example, reducing the number of phalanges is typical for modern golden mole, fingers that look like fingers dokofossora (Fig. 3). This is a typical example of a parallel evolution, i.e. forming an independent similar adaptations in different groups of animals, in this case – at basal mammals (dokodontov) and placenta.
Fig. 3. Evolutionary Tree dokodontov (A), the reconstruction of wood dokodonta Agilodocodon (B), its paw (C), floating dokodont Castorocauda (D), newfound digging dokodont Docofossor (E). Right (F) – comparison of the proportions of the phalanges in mammals living in trees (arboreal), do not live in trees all the time, but it's good climbing (scansorial), land-based (terrestrial), burrowing (fossorial) and underground inhabitants (subterranean). Shown fingers following animals (top to bottom): flying lemurs (Cynocephalus), lemur (Lemur), Agilodocodon, opossum (Didelphis), hedgehog (Erinaceus), a viper (Tachyglossus), Docofossor (BMNH131735), golden mole (Chrysochloris). The image of the article under discussion Qing-Jin Meng et al. in Science
The authors suggest that the basis for such convergence are common genetic mechanisms responsible for regulation of the limb development in embryos of terrestrial vertebrates. At the golden mole in the course of embryonic development in the future fingers formed the beginnings of the three phalanges, but then two of them (the proximal and middle) merge. In mice and humans the same phenotype (merger phalanges) sometimes occurs because of the disruption of the gene regulatory cascades that control tab of the joint between the phalanges. Among the regulators involved in this process include proteins BMP2 (bone morphogenetic protein 2), GDF5 (growth and differentiation factor 5) and several others. These regulators are likely to manage the development of fingers and Jurassic mammals, and similar variations in their work caused by mutations that lead to a similar phenotype changes – for example, to merge the phalanges.
Likewise, it explains the parallel evolution of another important feature – lumbar ribs and lumbar spine. Modern mammals lumbar vertebrae ribs there, and lumbar spine morphology clearly different from the breast-carrying ribs. Loss of lumbar ribs and separation of the lumbar considered an adaptation associated with increased mobility and flexibility of the back of the body and the intensification of respiration. According to the fossil record, in different groups of early mammals reduction of lumbar ribs (partial or complete) occurred in parallel and independently.
New findings have shown that this is true for dokodontov. In dokofossora, Castorocauda and other dokodontov has lumbar ribs, the size of which gradually decreases as it approaches the sacrum. It seems, the original (ancestral) condition tag for dokodontov and all mammals. However, the second newly discovered dokodonta, agilodokodona (See below.) Lumbar ribs No lumbar clearly distinguished from breast. This implies that the evolutionary lineage dokodontov, as in the other groups of early mammalian occurred independent reduction lumbar ribs.
The reason lumbar ribs easily lost, and sometimes may appear again, presumably lies in the fact that the genetic regulatory cascade manage bookmarks of ribs in embryogenesis, the same for all mammals. A key role is played by genes Hox9, Hox10, Myf5, Myf6 and others. Changes in the work of a small number of genes may be sufficient for a radical change in phenotype. For example, you can get the mouse embryos developed lumbar ribs, if you turn off all three copies of the gene Hox10 (see .: New fossil discovery sheds light on the early evolution of mammals, "Elements", 17.03.2007).
The second ancient mammals, called Agilodocodon scansorius («agile dokodont climbing"), found in the Middle Jurassic of Inner Mongolia (Fig. 4). This dokodont was also small (14 cm from nose to tail, the weight of 27-40 g). Judging by the structure of the spine and extremities, agilodokodon was well adapted to climbing trees. In particular, the proportion of his fingers point to the arboreal (Fig. 3). All other known dokodonty were either ground or floating (bobrohvost), or, as we now know, digging. Thus, the finding broadens understanding about the range of environmental adaptations dokodontov.
Fig. 4. Agilodocodon scansorius: reconstruction (A), drawing the skeleton (B), and a general view of the findings (C). The image of the article under discussion Qing-Jin Meng et al. in Science
The structure of the teeth agilodokodona indicates a mixed diet, which included not only insects and other small animals, but plant foods. On grounds such as the shape of the molars and the relief of the surface, similar to agilodokodon some lemurs, lorises and Galago – primates eat insects, fruits, gums, and plant juices. The similarity with primates can also be seen in the structure of the paws (Fig. 3), which is not so surprising when you consider that primates – originally a group of wood. Other dokodontov in the structure of molars is not so clear-cut signs of adapting to plant foods.
Cutters agilodokodona have an unusual shape: they look like a wide, pointed at the end of a shovel or a spoon, strongly convex on the outside (from the mouth) and concave on the inside (by the language). The authors note that the incisors are similar in some American monkeys: marmosets, spider monkeys, howler. These monkeys are used for gnawing incisors bark to get to the juice and sweet selections. Apparently agilodokodon also earn their living in this way.
New findings have shown that the ability to convergent evolution of similar systems of life forms and the parallel development of the same sets of ecological niches is typical not only for the "higher" terievyh mammals (marsupials and placental). This ability has had basal mammaliaformy who had to "invent" its lemurs, otters, moles and long before the heyday terievyh.
Harmful mutations are located in areas rarely recombining chromosome
Fig. 1. An example of chromosomal recombination occurring during the formation of gametes. Prior to recombination the DNA of each chromosome of the pair of homologous chromosomes is doubled, so that both chromosomes are composed of two spirals connected by a special structure – centromere (white ovals). Komplemntarnye spiral from different pairs of chromosomes can exchange areas: in the DNA strand breaks are formed, the DNA fragments are exchanged, and then the resulting hybrid chromosomes stapled.
Canadian researchers studied the distribution of harmful mutations in the chromosomes of man and found that the most likely harmful mutations can be found in areas of the chromosomes, which are rarely recombine. However, this effect was less pronounced in larger populations. It turns out that the more effective population size (the number of people participating in reproduction), the less delayed harmful mutations in the genome.
Sexual reproduction – is not the only way to create new combinations of genes. Bacterium, for example, may transmit another bacterium one or more of its own genes in a small molecule composed of DNA – plasmid. Also genes may be transmitted via viruses, if the assembly of viral particles in their capsid mistakenly fall DNA of the host cell. Finally, thanks to advances in bioengineering person can be added to the genomes of many different organisms, those genes that are deemed appropriate. However, sexual reproduction is one important feature – this recombination sites is exchanged homologous chromosomes, thereby producing not only new combinations of genes and hybrid genes in which a part will be derived from a single chromosome, a part – of another ( Fig. 1).
In somatic cells, organisms that reproduce sexually, all the chromosomes are presented in pairs. Chromosomes pair is not quite identical – they contain the same genes, but some of them may be represented by different variants – alleles. In addition, the chromosomes pair may differ random mutations, which inevitably arise with some frequency. In the formation of sex cells into each of them should get only one chromosome of each pair to the merger with a sexual partner cell embryo was a normal set of chromosomes, instead of twice. But before we disperse to different gametes, chromosomes pair exchanged some areas – this exchange takes place on the stage of meiosis. In males, meiosis begins to go after puberty and may last until his death, with one cell meiosis – sperm precursor is about 70 days. In women, sex cells, meiosis begins during fetal development, and is only completed after fertilization – that is, the female reproductive cell meiosis can last up to 50 years. During this time, the reproductive cells are formed that have a reduced amount twice chromosomes and chromosome germ cells become different from the parent.
Recombination in the formation of sex cells creates a basis for greater variability and helps to quickly weed out bad genetic variants. So, if an individual chromosome is inherited from the harmful mutation, it will be harder to live, it will leave fewer offspring or leave it altogether, resulting in a chromosome with deleterious mutations would be less common in the population. But imagine that on the same chromosome with deleterious mutations, there are beneficial mutations that, on the contrary, give special advantages and compensate the harm of harmful mutations. Because of this harmful mutations will not be discarded, or the selection will be rejected more slowly than it should. However, due to the recombination of the chromosomes are not related to each other forever, and sooner or later have harmful mutations do not prove helpful neighbors in the chromosome and it will be deselected selection. This is one of the reasons that the recombination is so important.
Another reason – Recombination allows you to receive a "good chromosome" (without harmful chromosome mutations) of the two "bad". For example, if both chromosomes pair have deleterious mutations in different areas, as a result of recombination one may get rid of the mutation and the second receive both. Of course, the other chromosome will be quite harmful, but the first chromosome will return to normal. And if possible to recombine not, chromosome never get rid of a mutation that arose in it.
Thus, Y-chromosome male couple which is very unlike her X chromosome can not recombine with the X chromosome, which is why in the Y-chromosomes are constantly piling up mutations that have already made many of its genes are inoperative, and with time the situation may become worse. For comparison, in the X-chromosome genes in 1400, and in the Y-chromosome – of less than 100, and in fact, these chromosomes once descended from a single precursor. Due to the fact that the Y-chromosome nowhere to throw an unfavorable mutation, it is not possible to "turn back", restoring the previous version of the chromosome by recombination. If by chance the individual will die a "good» Y-chromosomes, the "good" chromosomes can no longer be restored from fragments bad. Such an irreversible deterioration in the absence of gene recombination is called "Muller's ratchet."
Relatively recently it revealed that recombination takes place in different parts of chromosomes with different frequency (S. Myers et al., 2005. A fine-scale map of recombination rates and hotspots across the human genome). It was established by analyzing the distributions SNPs – single nucleotide substitutions of DNA specific to different people. If you put a lot of polymorphisms in the genome map, you can find that somewhere they were "shuffled" often, but somewhere – less. In addition, the frequency of recombination for different parts of the DNA can be measured directly – by comparing the genomes of a large number of parents and their children. If the chromosome of the first child is a parent's chromosomes, and then part of it to another chromosome – so between these sections recombination has occurred. Many of these events is marked on the map of the genome and see which areas of the chromosomes in recombination occurs more often, and in what – less.
The average frequency of recombination between single polymorphisms – somewhere in one case 2300 meiosis. For "hot spots" where recombination occurs more often, the frequency reaches one case per 80 meiosis. The existence of "hot" and "cold" regions of recombination due to different reasons. Firstly, the recombination does not go to the ends of chromosomes and in the centromere (constrictions that bind the two strands of DNA chromosomes after doubling). DNA in these areas densely folded, so proteins that help chromosomes recombine do not have enough space for action. These proteins are the most preferred free stretches of DNA where proteins found less competition and where DNA easiest approach. In addition, the proteins – assistants are not indifferent to the recombination of DNA sequences and some sequences of nucleotides to them more attractive than others. All this creates an uneven picture of the distribution of recombination sites on the chromosomes where some exchanges occur fairly frequently, but somewhere – less.
Given that regions of chromosomes recombine with varying frequency, scientists from Saint-Justine Hospital at the University of Montreal (Quebec, Canada) suggested that harmful mutations should focus where recombination occurs less frequently, and where the selection of a long time, "lacking." To do this, scientists otsekvenirovali RNA 1,400 people and are all the mutations found on maps of chromosomes. For each mutation they found out whether it changes the amino acid in the protein (because not all nucleotide substitutions leading to amino acid substitutions in the corresponding protein), can affect the function of the mutation of the protein and whether it is listed in the database of mutations that affect health. It was found that mutations that lead to the substitution of amino acids, often located in regions that are seldom recombined. Those who cause harm, and often located in less recombining regions, and less than recombination occurs at the site of the chromosome, the more likely there is to be found harmful mutations (Fig. 2).
Fig. 2. Enrichment rarely recombining mutations in chromosomal regions of French-speaking Canadians from Quebec (FCQ), European (EUR), Asians (ASN) and the African (AFR). Odds ratio – the ratio of chances to meet certain group of mutations in rare and often recombining recombining regions of chromosomes. The value of this parameter is greater than 1 means that the mutations are more common in areas rarely recombining chromosome. Rare – mutations occur with a frequency of less than 1%, Non synonymous – mutations resulting in an amino acid change in a protein, Damaging – mutations affecting the health of the data base ClinVar, Neutral – mutations that do not cause amino acid substitutions in proteins. Schedule of the article under discussion in Nature Genetics
However, with the increase in the effective size of the population, which belonged to the people, the effect of the accumulation of harmful mutations in the chromosomes recombine slowly become less pronounced. The effective size of the population – is a parameter that reflects the number of breeding animals; It is calculated from data on genetic variability and represents the size of the pool of genes available to the population. The effective population size is higher for Africans than for Europeans and Americans, because, as we now know, the entire population of the Earth occurred in Africa and in the process of resettlement in other areas has experienced repeated to myself the effect of the "bottleneck." Therefore, compared with Africa, other parts of the population of the Earth was a smaller number of people and its gene pool poorer. Through sexual reproduction, which was attended by more people in the African population to recombine more diverse set of chromosomes. In Africa, much less frequent partner with the same adverse mutations and such mutations will then selected, including less recombining regions of chromosomes.
So, on the one hand, the results of research are cause for optimism, as the world population grows and takes part in the reproduction of an increasing number of people. One would expect that due to the sexual reproduction, eventually harmful mutations will better be discarded from the genome. On the other hand, the population of developed countries is aging and the birth rate is falling in them, so it is difficult to say with certainty whether we will be healthier in the future. Whatever it was, the results are useful to researchers who are looking for mutations in the DNA, leading to disease: it is now clear that such mutations are more likely to settle in areas rarely recombining chromosome, so that their search should be accelerated.
The human race has become ancient and diverse
Fig. 1. A graduate of the University of Arizona hut Seyoum (Chalachew Seyoum) found a fragment of jaw oldest member of the human race during field work in his native Ethiopia in January 2013. Photo from azcentral.com
New discoveries have allowed to clarify the understanding of the early evolution of the human race. In the Afar region (Ethiopia) in the sediments of age 2,80-2,75 million years found a fragment of the lower jaw, referred by American and Ethiopian paleoanthropologists to the genus Homo. Until now, the oldest find of Homo considered upper jaw AL 666-1 age of 2.33 million years. Meanwhile, another team of anthropologists from the United Kingdom, Germany and Tanzania pereizuchila type specimen of Homo habilis (OH7, age of 1.8 million years) and came to the conclusion that early Homo still better to refer to three different species (H. habilis, H. rudolfensis and "early H. erectus»), but not to the same polymorphic species, as suggested by scientists studying early erectus in Dmanisi (Georgia). Three alleged species differ in the structure of the jaws and teeth, but hardly distinguishable on such an important feature as the volume of the cranium, which has been extremely volatile in all three. Either way, the new data show that the genus Homo appeared and began to diverge earlier than previously thought.
The results of two major paleo-anthropological studies published in early March in the journal Nature and Science. Both works shed light on the early stages of evolution of the human species (Homo).
The article of the British, German and Tanzanian anthropologist, published in Nature, are considered new, more accurate reconstruction of the type specimen Homo habilis OH7 (age of 1.8 million years), found in 1960 at Olduvai Gorge in Tanzania. Studied material includes a slightly deformed lower jaw with teeth and two fragments of parietal bones. The authors studied the priceless discoveries using X-ray computed tomography. Understand the structure of posthumous cracks and deformations, scientists reconstructed the shape of the jaw and parietal skull with the maximum possible accuracy.
Comparing the reconstructed jaw (Fig. 2) with other known jaws of early Homo and Australopithecus, and modern humans, chimpanzees and gorillas showed that jaw OH7 «primitive», that is, has a number of archaic features, brings it closer to Australopithecus. This applies primarily to the shape of the dental arch (Fig. 3). For jaw OH7 characterized by long, almost parallel rows of premolars and molars. This suggests a strong prognathism. In other words, the jaw of the individuals on the monkey came forward. Meanwhile, the known finds of early Homo, including those older than OH7, whose jaw had a more "human" appearance. For example, the upper jaw AL 666-1 age of 2.33 million years old, which is still considered the most ancient finding Homo, dental arch is shorter and wider and the tooth rows are not parallel but diverge like the more advanced members of the human race.
Fig. 2. The lower jaw Homo habilis OH7. Left – jaw in the initial state. Different colors show fragments, the relative position of which has been changed in the course of reconstruction. In the center – a three-dimensional reconstruction, based on the correction of post-mortem deformation. Right – another reconstruction, in which the right half of the jaw restored as a mirror image of the left, and third molars ("wisdom teeth") as a copy of the reconstructed second molars. The length of the scale interval of 2 cm. The image of the article under discussion in Nature
Statistical analysis of the variability of the shape of the dental arch in various representatives of humanoid showed that early Homo range of variability for this trait greatly exceeds anything that can be observed within the same species in modern apes, including humans. For example, the jaw KNM-ER 1482, traditionally assigned to the species Homo rudolfensis, different from OH7 almost as much as the jaw of modern man from the jaws of chimpanzees.
After analyzing the pairwise intra- and interspecific differences in dental arch form in different hominids, the authors came to the conclusion that on the basis of early Homo is quite clearly divided into three clusters, which they tend to be interpreted as three different species: Homo habilis, Homo rudolfensis and early Homo erectus (the latter includes, in addition to the African finds, also people from Dmanisi). In this case the shape of the dental arch habilis more "monkey" (almost to a greater degree than in the Afar Australopithecus), while rudolfenzisov and erectus – more "human" (Fig. 3). Thus, the authors of the article under discussion do not agree with David Lordkipanidze and his colleagues, who on the basis of new data on the skulls from Dmanisi suggested to be one of the earliest Homo choppy sea (see Fifth .: Dmanisi skull showed enormous scope of individual variability of early Homo, «Elements "10/21/2013).
Fig. 3. Comparison of the form of the dental arch of the lower jaw in modern and fossil hominoids using principal component analysis. Different colors highlighted areas corresponding to the modern anthropoid: H. sapiens (modern man), Pan (chimpanzees), Pongo (orangutans), Gorilla (Gorilla). The points that fill the space between modern apes and humans, fossil hominids match. By referring to H. habilis specimens referred OH7, OH13 and ER1802. Jaws AL822, AL400, AL288 Australopithecus afarensis belong; D2735, D2600, D211 – early erectus Dmanisi; ER60K (ER60000), ER1482 – members of the species H. rudolfensis; KP29281 – early Australopithecus A. anamensis. Drawing from the discussed article in Nature
Of course, this conclusion should not be considered final. It is based on a small number of finds and morphological characters. In addition, not all the findings of early Homo fit well into the proposed scheme. For example, the authors note that copies OH65 (1,6-1,8 million years) and the aforementioned AL 666-1 (2,33 million years), usually referred to H. habilis, too much different from the type specimen and OH7 They fit into their concept habilis. These instances are also deprived of the specific characteristics of the front part of the skull, characteristic of H. rudolfensis. The authors admit that they may be, must reconcile with the earlier erectus, but abstain from the final conclusions and leave the question open.
The researchers also calculated the volume endocast (inner cavity of the skull) OH7 based on surviving fragments of the parietal bone. The calculations are based on two alternative ways of parietal reconstruction of the skull and two ways of calculating the volume of the brain in the form of this section, with the result that happened four digits. All are in the range from 729 to 824 cu. cm, which significantly exceeds the previous estimates (647-687 cu. cm) Thus, OH7 had a very voluminous (at the time) the brain, which, oddly enough, combined with the powerful, strongly raised "monkey" jaws. This combination of features is not very consistent with the known hypothesis that the weakening of the jaw and chewing muscles in early Homo was an important prerequisite for the growth of the brain.
New data, along with the previously obtained show that early Homo was characterized enormous range of variability in terms of the brain. Alleged 'species' early Homo on the basis of indistinguishable: the ranges of variability almost entirely overlap (Fig. 4).
Fig. 4. Two alternative reconstruction of the crown of the skull and estimate the amount of OH7 endocast in various representatives of early Homo. The red color shows the estimates based on new reconstructions OH7 (black – old reconstruction). Drawing from the discussed article in Nature
These results are somewhat changing ideas about the early evolution of the genus Homo. Anthropologists will long debate about the classification of these forms and how you combine them into a single view or share a few. From an evolutionary point of view it is a question not of principle. In any case, one can hardly assume that early humans lived at the same time in the same territory in East Africa, divided into distinct, reproductively isolated groups that never crossed each other. Apparently, we have a typical picture of the initial stages of rapid morphological divergence, like barbs (barbels) Lake Tana (14 shapes formed there in less than 30 000 years, some ichthyologists consider different types, others – a kind) or cichlid large African lakes (see .: The genomes of African fish clarify the mechanisms of rapid speciation, "Elements", 09.29.2014). Moreover, this divergence was due to start long before the era when he lived OH7. It should, in particular, from the fact that the jaw OH7 more ancient primitive jaw AL 666-1. So, already 2.33 million years ago, most likely at the same time there were representatives of the human race, vary greatly in the form of the dental arch. Apparently, a common feature of all populations (or species) of early Homo was a high variability in the size of the brain: some individuals are almost did not differ in this parameter from the ancestors, Australopithecus, while others were much more brainy.
The assumption of an early start of the divergence of the genus Homo is consistent with the new discovery, described in the article of anthropologists from the United States and Ethiopia (Fig. 5).
Fig. 5. Jaw oldest member of the human race LD 350-1 and a map of the area of the Afar in northern Ethiopia. Locations hominid and stone tools are marked with asterisks. Discussed finding comes from a location Ledi-Geraru. The length scale of 1 cm segments. The images of the discussed items B. Villmoare et al. and A. Gibbons in Science
A fragment of the lower jaw of ancient Homo was found in January 2013 in the region of Afar (Ethiopia), at the seat of Ledi-Geraru, which still did not find fossil hominids, despite diligent search. In the 30-40 km from this place are the famous location Hadar, dikika and Gon, which found numerous fossil remains of australopithecines and early Homo, as well as ancient tools 2.6 million years of age.
The deposits, which are found in the jaw, enclosed between two layers of volcanic tuff, which managed to date by radiometric methods. These dating, along with biostratigraphic and paleomagnetic data allow reliably determine the age of the jaw: 2,80-2,75 million years. Thus, the owner of the jaw later lived past Afar Australopithecus (the youngest finds of A. afarensis have an age of about 3 million years old) and much earlier than the oldest Homo from Hadar (2.33 million years).
Of course, a piece of jaw with six teeth (canine, two premolars and three molars) – it is a little. But the bone and teeth are well preserved, which allowed researchers to more or less convincingly justify their bold decision include the discovery of the genus Homo (rather than Australopithecus). Authors scrupulously sorted differences between their findings, which received the code name LD 350-1, from the Australopithecus (especially from A. afarensis, which find a marked similarity) and Paranthropus. Most of the features that distinguish a copy from the LD 350-1 Australopithecus, brings him to the people.
Fig. 6. Comparison of Australopithecus afarensis jaw AL 822-1 (left) and the oldest Homo LD 350-1 (right). Image of the additional materials for discussion article B. Villmoare et al. in Science
The most important features are shown in Fig. 6 where the jaw LD 350-1 is compared with the jaw A. afarensis. Australopithecus mental foramen (mental foramen), serving for the passage of nerves and blood vessels (indicated by the red arrow), opens up towards the front and at the bottom of recesses on the side of the jaw (edge recess is outlined in yellow dotted line). At LD 350-1 groove is missing, the corresponding portion of a convex surface, and the mental foramen was called back (as many Homo). In A. afarensis branch of the lower jaw (ramus mandibulae) – large angular plate extending upward from the body of the bone – begins opposite the second molar (M2), whereas the LD 350-1 cutting edge branch shifted back and begins in front of the third molars (M3 ). In addition, the height of the jaw LD 350-1 is approximately the same throughout (as in most Homo), while in the most massive bone Australopithecine front (has a greatest height bicuspids) and tapers behind (under its height lower molars). There are other signs that indicate proximity to Homo. These include the nature of the attrition of tooth enamel and the slope of the outer (buccal), the edges of the molars: in Homo these edges are nearly vertical, Australopithecus, usually beveled.
The shape of the dental arch at the LD 350-1, judging from the debris was primitive, about like H. habilis OH7 (but not like older AL 666-1).
Despite the differences from Australopithecus and some resemblance to Homo, jaw LD 350-1 is hardly a typical jaw early Homo. It has archaic features and is different from habilis jaw and rudolfenzisov. According to the authors, this jaw looks exactly as it should look like the jaw of a transitional form between Australopithecus afarensis and later people like habilis or rudolfenzisy. So LD 350-1 could, if desired, be attributed to the genus Australopithecus (and certainly there is no guarantee that other parts of the skeleton of the Undiscovered individuals were just as "human" as the lower jaw). A similar dilemma faced by paleoanthropologists whenever forms are transitional between previously isolated genera and species. Making Choices sometimes have to almost throw a coin, although scientific articles and is not accepted to write about it (see .: Australopithecus sediba – Australopithecus, like the man, "Elements", 15.04.2010; note that a decisive argument in favor of the classification A . sediba australopithecine was a small cranial capacity, the size of the brain have been the owner of the jaw LD 350-1, unknown). Nothing so vividly and clearly shows no loyalty to the Darwinian idea of gradual evolution, like those suffering paleoanthropologists trying to draw clear boundaries between the transition smoothly into each other's views.
Apparently, already 2.8 million years ago, some Australopithecus, similar to A. afarensis, began to evolve into a "human" side – at least in regard to the shape of the jaws and teeth (which they had arms, legs, brains and behavior, we do not know). With this idea in agreement previously found scattered teeth of similar age, including eight teeth KNM-ER 5431 (2.7 million years) of Koobi Fora in Kenya.
If this hypothesis is confirmed by new findings, and indeed it appears that early Homo descended from A. afarensis, you have to admit that some similarities with humans, marked by later representatives gracile australopithecines, such as A. garhi especially A. sediba, is the result of parallel evolution.
Judging by the concomitant fossil fauna, the alleged ancient man lived LD 350-1 in an open and fairly dry place, like a modern African savanna, possibly with gallery forests along the banks of reservoirs. This follows from the abundance of herbivorous mammals and the lack of wood. The possible presence of gallery forests indicate bone deinotherium; fossil of fish, crocodiles and hippos show many ponds. These data are consistent with the accepted views on the importance of climate change and the spread of savannah in the origin of man (see .: The influence of climate on human evolution is confirmed, "Elements", 07.02.2011).
Tsianosulfidny protometabolizm – a recipe for life on earth
Fig. 1. We did not have any tangible evidence of Katarchean, but logic and experiments help us to imagine the world of the young. Image source the-scientist.co
RNA world preceded time prebiotic synthesis when born anyway necessary for replication of the molecule – nucleotides, proteins, lipids. First we consider the process of chemical synthesis alone. Now in the laboratory John Sutherland found path that leads to the synthesis of a considerable range of biological molecules. No need to guess what it was before, RNA or proteins – they probably were synthesized simultaneously in a single cascade of chemical reactions; it appears at the beginning of hydrogen cyanide and hydrogen sulfide with metal catalysts. This network of reactions authors called tsianosulfidnym protometabolizmom. With the release of new research we can talk about a turning point in the science of the origin of life.
John Sutherland (John Sutherland) with the team from the Laboratory of Molecular Biology Research Council for Medicine at the University of Cambridge (UK) continued their fascinating study of the first stages of the origin of life – the appearance on the planet of biological molecules. About five years ago, they described a simple way of synthesis of pyrimidine nucleotides, most of those who could not manage to get out of simple substances (see .: chemists have overcome a major obstacle on the way to the abiotic synthesis of RNA, "Elements", 18.05.2009). This required a heated nitrogen bases (Cyanamid) along with sugar (glycolaldehyde) tsianoatsetilenom and in the presence of phosphoric acid under ultraviolet irradiation. As a result, the wonderful, albeit understandable way for chemists obtained pyrimidine ribonucleotide – cytidine and uridine. And while a high final yield of the product, in substantially purified form of impurities, since other reaction by-products are unstable to UV radiation (Fig. 2a, this shows part of prebiotic chemistry blue arrows).
All those involved and interested in the early evolution of life, were delighted. Among emotional endorsements sounded quite sensible questions: where to take the early Earth glycolaldehyde in large quantities? – Yet it is not quite a simple matter. For three years the team Sutherland managed to solve this problem (D. Ritson & JD Sutherland, 2012. Prebiotic synthesis of simple sugars by photoredox systems chemistry) – and again, elegant and affordable. Chemists synthesized glycolaldehyde and glyceraldehyde of hydrogen cyanide; the reaction proceeds in the light and in the presence of cupric sulfide. But what was the joy of scientists when they found as side (!) Reaction products of α-aminonitrile synthesis – the precursor amino acids glycine, serine, alanine and threonine (D. Ritson & JD Sutherland, 2013. Synthesis of Aldehydic Ribonucleotide and Amino Acid Precursors by Photoredox Chemistry). Fig. 2a shows the path of the green arrows.
Of course, it was impossible to stop: it is clear that detected a network of reactions – is a gold mine prebiotic synthesis. And the same winged team became more study of the reaction product mixture of hydrogen cyanide, hydrogen sulfide, phosphates and various divalent metals.
First and foremost, it was decided to consider further the transformation of glyceraldehyde phosphate buffer – was theoretically a more stable three-carbon isomer. Indeed, he was found: glyceraldehyde gradually but in good yield (59%) was converted into dihydroxyacetone. And that, in turn, in the presence of hydrogen sulfide in the light is split into acetone and glycerol. Having these substances, chemists scented victory – to lipid synthesis remains quite a bit. And if the resulting mixture to heat up (and we remember that the process is in phosphate buffer) with the catalyst (zinc), the flask would be glycerol-1-phosphate and glycerol-2-phosphate – precursor lipids. The yield of these products was impressive: an amount of 71%. And if alternate light and darkness, that occur one after the other (as a nice supplement) conversion reaction of acetone in the amino acids – valine and leucine.
Then, it turned out that of acetylene and hydrogen cyanide in the presence of various copper compounds and hydrogen sulfide may also be synthesized amino acids arginine, proline, asparagine, aspartate, glutamine and glutamate. And by the way, a necessary product in the conversion of hydrogen cyanide in the presence of an amino acid is cupric cyanoacetylene, the same one that was in demand for the synthesis of pyrimidine.
That's a real primordial soup, or, if you prefer, a hypothetical warm pool! John Sutherland and his colleagues are now imagine this ancient pond zhiznerodny much clearer than anyone else. This warm pool became overgrown chemical realistic detail. Chemists have put it during Katarchean when our planet has experienced the hard way all the hardships of late meteorite bombardment. Here's how it could happen.
In collisions carbonaceous substance meteorites coalesced with atmospheric nitrogen, as a result of the high temperature reaction, hydrogen cyanide is synthesized. From meteorite schreibersite – iron-nickel phosphide – with high energy of impact of events results in phosphates. In the presence of water (here it is – the warm pool!), Hydrogen cyanide dissolved and combined with iron to form ferrocyanide. There also were washed chlorides, soluble compounds of sodium, potassium and calcium – all that in abundance was the young Earth. When the puddle evaporates, and she had to evaporate due to the high surface temperature of the planet and meteorite bombardment, heated ferrocyanide and interacting with the potassium, sodium, calcium form the corresponding cyanide, carbon and carbides. This layer of solid salts only promising, since their dissolution and heating is a set of necessary for "life" of ingredients: hydrogen cyanide, cyanamide, acetylene. The latter is formed by dissolving in water the calcium carbide. Phosphates and hydrogen sulfide are included.
To broth was prepared, our pool was dry and again periodically filled with water periodically illuminating and sometimes dive into the darkness. And then it itself could go once all the necessary synthesis of biomolecules: nucleotides, amino acids, lipids. Scientists have proposed a network of interconnected reactions, and even if the start is given, the output will turn the whole set. There is no need to guess what it was before – amino acids and proteins or sugar ribonucleotides. Everything was right. The warm pool – it is hot and becoming dry pond filled with cyanide and hydrogen sulfide, hard UV lit: welcome to life!
Chemists still have serious work to unleash all the nodes of the network of chemical, but the main thing – that the gap between simple organic molecules and the molecules of life is no more. Now there is a bridge that chemists call tsianosulfidnym protometabolizmom. Probably, this term will very soon become fashionable, popular and very meaningful.
Physicists exploring the dark forces and other dark events
Penguins in elementary particle physics: regular, light penguin (left) and new, dark Penguin (right), which appeared in the literature only a couple of weeks ago. Images from the site and from the article quantamagazine.org R. Primulando, E. Salvioni, Y. Tsai, 2015. The Dark Penguin Shines Light at Colliders
Recently, the headlines of scientific publications on elementary particle physics blossomed words "dark forces", "Dark Sector", "dark radiation" and even "dark penguins." Such a surge of interest in a variety of dark events may indicate that particle physics is on the verge of the largest opening for a long time.
Scientific revolutions are not always begin with a loud opening. It happens that the idea at first appears only as an amusing hypothesis for some time discussed by theorists – discussed so casually, without forcing anyone and without attracting much public attention – and then, under the weight of irrefutable evidence and theoretical developments, it becomes suddenly a new paradigm. So famous is now going through discoveries in physics of the XX century; It seems that something similar is happening now. Although it is not too advertised in popular science publications, but if you look closely at the titles of articles on the physics of elementary particles, we can see constantly flashed the word "dark" to the public in unusual phrases.
We are not talking about dark matter or dark energy – those are the substance has long been at the hearing. We are about something new: the dark forces (dark force) and other dark events. The number of scientific articles devoted to them is growing like an avalanche. Well, if it were only theoretical fantasy. But it has now put some experiments on the dark force at the Tevatron, the Italian DAFNE accelerator and accelerator centers. Dark force now trying to see even in the center of our galaxy.
Further more. Where the dark forces out there and dark radiation (dark radiation). Dark matter, flying in space and radiating electromagnetic waves dark – it is now quite mundane topic of a scientific publication. Hints of this dark radiation is, among other things, show through in astrophysical data. It is also possible that the source of dark radiation in the present universe are dark stars; however, on this occasion there is no consensus yet physicists.
One way or another, but to replace the boring dark matter comes to a dark sector (dark sector), which unfolds its, dark, life. According to the latest scientific publications, physics literally rushed to study this new side of the world – articles on Dark Sector, estimated hundreds. How do you like the dark core, the signals from the dark atoms and anti-atoms dark? A dark photons and dark Higgs bosons, which are now looking at colliders? Incidentally, the Large Hadron Collider, which will soon begin a new session will also be aimed at the study of the dark sector – a physics already talking loudly.
All the rage in this scientific direction – a dark Penguins (dark penguins), which are discussed in the appeared two weeks ago, the article The Dark Penguin Shines Light at Colliders. Of course, these are not real penguins, but "made" of heavy elementary particles. But this dark penguin can be the first sign of the new jamb dark effects that physics is about to discover. And who knows, maybe in the really existing dark worlds controlled by dark forces will light (or dark?) Dark stars and planets in the dark will emerge dark life up to this dark penguins? Modern physics is looking for answers to these questions are dark.
Why is the gene that causes early abortions are not weed out the selection?
The five-day embryo (blastocyst) rights. At this stage, well-read by aneuploid errors resulting from improper chromosome segregation during mitosis. To study the effects of aneuploidy researchers used a three-and five-day blastocyst. Photo from bag.admin.ch
US experts to investigate the causes of aneuploidy in human embryos. It is known that aneuploidy – non-multiple number of chromosomes or their parts – causes rapid destruction of embryos and early miscarriage is the main cause of reduced fertility in women. As it turned out, aneuploidy is associated with a specific polymorphism in a specific area on the fourth chromosome. This polymorphism is associated with a gene topographically PLK4, responsible for chromosome segregation during mitosis. It is surprising, but the option PLK4, causing reduced fertility, is widespread in the human population, its rate is quite high. Scientists are discussing the question of how could seemingly harmful gene spread in the population, and not drop out selection.
Experts from Stanford University and the company's genotyping Natera dismantled interesting case of fixing harmful trait in human populations. "Harmful" – means reducing reproductive success. In this case, reduced reproductive success was not a remote consequence of a harmful trait, such as low resistance to disease or gender unattractiveness, and a direct result of reducing the quality and survival of embryos. Scientists interested in the number of defective chromosomal regions – so-called aneuploidy cases when part of a chromosome (or an entire chromosome) or is lost or present in duplicate. Such errors occur during meiosis or mitosis when proper chromosome segregation violated the daughter cells. It is known that aneuploidy causes the death of the embryo in the early stages of development and miscarriages. In their study, the researchers assessed the level of aneuploidy in eggs and early embryos and found out what has caused the emergence of such errors.
Much of the effort was spent on finding out the time of occurrence of aneuploid errors. Clearly, they can appear as in meiosis as in mitosis. In the first case aneuploid chromosomes will be found in the unfertilized egg, the second – in early embryos. Experts worked with samples of artificial insemination: eggs, sperm and early embryos at the blastocyst stage. When the art PCR was possible to read the genomes of parental cells and embryos. This material – it should be noted, quite massive – allowed to estimate the proportion of aneuploid and other types of errors. The reasoning was approximately as follows: since the errors in aneuploid sperm during meiosis extremely rare (as it is known), all the errors in the paternal genome of the embryo can be attributed to mitotic abnormalities.
Mitosis in the early stages of embryonic development is regulated by maternal genes, so it's possible that an error chromosomes are responsible or that maternal genes. Having data on maternal genome, you can look for these unfortunate genes. To do this it was necessary to compare genomes of nuclei which have appeared in aneuploid errors, with those where no error occurred. And thus revealed a plot for the fourth chromosome variations which correlate maternal with aneuploidy embryos. Features of this site indicates that it is under strong influence of dynamic selection: there are signs of the so-called "sweeping through the selection of polymorphism" (see .: Selective sweep). One of the genes located in this area, – Polo-like Kinase 4 (PLK4) – has been well studied, and its function is related to the regulation of mitotic spindle formation and, consequently, the differences of paired chromosomes into the daughter cells. This gene Doctors excellent candidate for the role of the offender that order.
Check the available databases and private data collected by scientists showed that the "harmful" (increases the likelihood of aneuploidy in embryos) version of this piece of DNA is extremely common in a variety of human populations (with a frequency of 20% to 45%). All peoples have this genetic variant. It is interesting to note that it is not found neither Neanderthal nor denisovtsev.
It turns out that the genetic embryonic aneuploidy – the property is clearly unprofitable for reproductive success – in fact spread quite widely in the human population. It appeared, presumably, after the separation line and was supported sapiens selection. On average, people have only 30% of conceptions leading to successful pregnancy, and most of the failures are due to aneuploidy.
Why selection favored the spread of the harmful trait? Speaking about this, the scientists put forward a number of hypotheses. The first sign may be harmful, but it turned out to be linked to another feature, the benefits of which exceeds the harm of aneuploidy. Second, the harm from reduced fertility, probably not so great for the human population.
Scientists offer a version of balancing selection. They are based on the fact that the frequency of this allele is more or less similar in all human populations. This means that in this case, triggered some kind of common patterns. For example, scientists believe, reduce the likelihood of pregnancy, as well as concealed ovulation and constant readiness of females to mate, it led to the fact that males were more difficult to determine who is the father of the offspring, and therefore more males to invest in taking care of it. But, unlike the hidden ovulation and constant readiness for sex, this feature is still a negative impact on reproductive success. Therefore, it does not fully entrenched, it balances and fills allele does not cause aneuploid disorders. Women with enhanced ability to reproduce, thus enjoy the benefits sought by mothers with low probability of pregnancy.
It should be noted that such a scenario is balancing selection – only one possible, and American experts do not insist on it. Anyone can come up with a scenario for balancing selection. For example, it can be assumed, and this: a mother who rarely bear and give birth to children, keep better health and, therefore, have more options and power to take care of the offspring – as his and his sisters, and even grandchildren. After all, the health of the woman, the more likely that she will see her grandchildren and help them to grow – who doubt the benefits of grandmothers!
The artificial extension of daylight leads to obesity
Driving the impact of lighting on the deposition of fat. What we call the fat reserves, deposited in the white fat (open circles in the lower part of the figure). The white fat deposited those lipids that are not burned in brown fat (brown circles in the middle of the figure). Absorption is governed by lipid brown fat suprachiasmatic nucleus (as depicted in hours), which in turn reacts to light. In the center of the figure shows that noradrenaline (NA) signals from the suprachiasmatic nucleus and affect lipid absorption brown fat, and the rate at which they are burned (it depends on the amount of protein Thermogenin (Ucp-1), as well as the activity of the hormone-dependent lipase (HSL)). Drawing from the discussed article in PNAS
Dutch researchers have demonstrated a mechanism by which an artificial increase in the light of the day creates a predisposition to obesity. It turns out that under the action of light suprachiasmatic nucleus less actively stimulates brown fat to absorb and burn lipids. A less lipid burning brown fat, the more fat is deposited in white.
Thanks to the invention of electricity, we can choose their own mode and not depend on the change of light and dark periods of the day. Many people awake at night – either because these are the conditions of their work, or because they prefer this mode. Light day for waking people at night as it is extended – to the usual bright hours of the day are added to the artificial. A recent large-scale study involving 100,000 women found that this way of life is harmful for rather unexpected reasons: women who spent the night under artificial lighting (because either awake or sleeping in a lighted room), obesity is often observed (see. E . McFadden et al., 2014. The Relationship Between Obesity and Exposure to Light at Night: Cross-Sectional Analyses of Over 100,000 Women in the Breakthrough Generations Study). These interesting results can come up with different explanations. First, if a person is at night by the light, the more likely he is awake, because I prefer to sleep with the light, only a small percentage of people. We can assume that people awake at night eat more (many people know what to eat at night – it's a special pleasure) or less exercise (night – not the most convenient time to perform jogging or fitness club).
But whether obesity occur not because of the indirect effects of regime change, but because of itself increase the light of day? Dutch scientists decided to conduct an experiment on mice to test does not cause an artificial lengthening of daylight hours some changes in metabolism due to which there is a predisposition to obesity.
Scientists have reason to think that a change in the light of day can affect metabolism. It is known that the suprachiasmatic nucleus in our brain monitors the light cycle, and sends signals to the periphery, so that all cells of the body can adjust its internal clock. In accordance with the readings of clock changing intensity of many important processes – for example, the uptake of glucose, which is dependent on insulin sensitivity, which in turn varies with the progress of the biological clock (day insulin sensitivity is lower than the night). Depends on the time of day and the number of synthesized proteins, phospholipids and DNA – the parameters that are important for all cells without exception (day processes of synthesis of these molecules are more active than at night).
Conclusions about the mode in which the body must work today, the suprachiasmatic nucleus making based on signals of the light coming from the cells of the retina. It would be natural to assume that because of the night-time lighting suprachiasmatic nucleus falls into error and sends signals to the cells to work in "day" mode, although the body at this time is assumed to sleep. And these signals man nocturnal receives day and night, and because of that he can "float" the regulation of many processes.
In the experiment, the mice were divided into three groups: the first group of dark and daylight were of equal duration, in the second light day was extended (and lasted 16 hours), and a third day lasted all day. In mice, there was a similar situation: the longer was their daylight hours, the more fat they postponed (after 5 weeks, the mice that lived under constant illumination, were one and a half times thicker than the mice in which daylight is equal to night). Mice can eat as they wanted, but it was found that mice with a 16-hour light day ate no more mice 12 hours, the mice that lived under constant illumination, ate at all the least. It turns out they have a obesity is not due to overeating. Total time activity in mice at the extended photoperiod did not decrease, so that the lack of movement was not the cause of weight gain.
It remains to find a mechanism by which the length of daylight could affect the metabolism. There is no doubt that this involved the suprachiasmatic nucleus of the body as the main pacemaker. Indirectly, this area of the brain affects all body cells, but the direct links it forms not so much. It is noteworthy that the suprachiasmatic nucleus is directly related neural pathways with brown fat – tissue that burns lipids to receive heat and warm the body. In contrast, white fat cell, which stores lipids brown fat cells actively combusted these molecules in numerous mitochondria. Interestingly, the brown fat cells originate from the same precursor as muscle cells, and in some ways resemble them, they should also not store and process reserves, producing heat (and muscle cells produce useful work).
Scientists have suggested that the lengthening of daylight suprachiasmatic nucleus regulates the wrong brown fat and burns it is not so much lipids as it could. To test their hunch, the researchers tracked the tagged lipid molecules in experimental animals. It turned out that the extension of daylight brown fat absorbs lipids from the blood less. To test the role of the suprachiasmatic nucleus in the process, the scientists cut in experimental animals neural pathways from the brain to this part of the brown fat. After such an operation has become brown fat to absorb up to five times less than the lipids from the blood. It turns out the signals from the suprachiasmatic nucleus to stimulate brown fat to absorb lipids. Day of such signals receives less (normal brown fat is to burn lipids at night, when it's cold). And if the brown fat absorbs less of lipids, the large number of them will be delayed in normal white fat.
In addition, in the daytime in the brown fat decreased expression Thermogenin and decreased activation of the enzyme hormone-sensitive lipase. It turns out that afternoon brown fat not only absorbs less of lipids, but also burns them less active. And Thermogenin expression and activation of hormone-sensitive lipase dependent on norepinephrine signals from the suprachiasmatic nucleus. That is, the longer daylight hours, the less brown fat burns lipids and the more their stores of white fat. Thus, the length of daylight affects the rate of accumulation of fat reserves.
It should be mentioned that during the year daylight naturally changes, the stronger the farther away from the equator is a point of our planet. In December, for example, on South Pole (and the surrounding area to the south of 23.5 degrees south latitude) day lasts all day (and at the North Pole this month, on the contrary, the sun is not visible at all). People who live in these conditions, the progress of the internal clock is disturbed and may manifest insulin resistance and increases the amount of triglycerides (a type of lipid) circulating in the blood (see .: J. Arendt, 2012. Biological rhythms during residence in polar regions). These factors may contribute to obesity, but accurate data on how predisposed thereto explorers working with "broken clock", we do not. Due to the harsh living conditions at the poles of the people, on the contrary, likely to lose weight. In any case, the change in weight – it is not the main problem of those who work in the polar night and polar day; much trouble for them, sleep disorders and depressive disorders (similar to normal seasonal depression, see. Seasonal affective disorder). Therefore, the need to adjust the length of daylight by artificial means in such cases, when the situation is far from normal, no one doubts.
Hundreds of human genes still can replace similar genes of yeast
Fig. 1. The share of non-essential (yellow) and essential (blue) genes among the investigated pairs of orthologous genes of yeast and human for 12 classes of metabolic pathways database KEGG (KEGG PATHWAY Database). The image of the article under discussion in Science
Despite the fact that human and yeast divides a billion years of evolution, they have hundreds of genes with a common origin and functions. It turns out that about half of human genes are still able to replace the corresponding genes of the yeast. Thus predict substitutability on sequence similarity or level of gene expression was generally impossible. But, oddly enough, it was possible to predict the substitutability, knowing what the process involved gene. For example, the genes responsible for the initiation of DNA replication, were indispensable, and almost all of the genes in yeast sterol biosynthesis successfully replace human variant.
For most genes of any organism (70-80%) can be found orthologs (see. The homologous DNA sequence) – with the same genes origin – the others, even fairly distant organisms. Orthologous genes are not required to perform the same function – in different organisms, they can take on different roles. Especially it has this gene duplication, followed by one of the copies can be freed from the pressure of selection and try his hand at something else. Nevertheless, the function of orthologous genes often still remains the same. Organisms usually no reason to change something that works and so, especially if it is something produced in large quantities. Therefore, the genes change slowly non-coding sequences, and is actively working genes – even slower.
And yet, as far as could be different from orthologous genes for billions of years after they were separated from a common ancestor? Scientists from the University of Texas at Austin decided to check it quite straight-line method. They chose the 469 orthologous genes that were present in yeast and humans (and, moreover, in a single copy, in order not to complicate the picture), and check which of the human genes is still suitable for the yeast – after a billion years of separate development.
First, for each of the selected genes were obtained a yeast strain in which the gene has been switched off or even removed entirely. The genes chosen for the experiment such that without them, the yeast could not grow. The resulting strains were introduced special yeast plasmid with the corresponding human gene that is either continuously worked or could be included with the addition of certain substances. Sometimes, expression of the human gene had to be adjusted to an appropriate protein did not accumulate in toxic amounts. As a result, almost half (47%) of the disabled or deleted genes of yeast was able to replace the human homologue. It would seem that a man is quite far away from the yeast – but nevertheless a considerable part of his genes tested are still suitable for yeast.
It was interesting to find out what is common in the human genes and yeast that were replaced. The researchers evaluated 104 features that could affect the ability of genes to replace each other. Among them were the sequence similarity, protein and RNA accumulation and their size, the rate of transcription and translation, and many other parameters (characteristics were taken from the databases of biological KEGG – Kyoto Encyclopedia of Genes and Genomes; Fig. 1). As expected essential had sequence similarity, but in most cases it is not possible to predict whether the gene will suit a person to replace yeast orthologue. Unlike most genes (less than 20% of the amino acids encoded by coincidence) could not really replace the corresponding genes of yeast, and the most similar (more than 50% of the amino acids encoded by coincidence) most suited as a replacement. However, most studied gene into the intermediate area – from 20 to 50% similarity encoded amino acids – and the similarity of sequences can not be predicted, whether human protein suitable as a substitute for the yeast.
Unexpected is that substitutability gene could not be predicted and the level of expression – in fact the more active the gene works, the more risky to change it and the slower it evolves. One would therefore expect that the highly expressed gene, the more likely it will be able to replace the orthologous gene is a member of another species, but in general, this pattern was not observed.
But also unexpectedly substitutability orthologous genes can be predicted by knowing the process, which involves their products. Thus, the human genes involved in the initiation of DNA replication, did not fit the yeast and nearly all of the sterol biosynthesis genes (see. Sterol) – catalyzing transition acetyl coenzyme A cholesterol in humans and ergosterol (see. Ergosterol) yeast – approached.
Interesting was the pattern with the proteasome genes – a molecular machine to destroy unwanted proteins. Proteasome is composed of several proteins rings stacked. External rings are composed of alpha subunits, and they are controlled by the gate of the proteasome and that fall inside it. Ring in the middle consists of beta-subunits are capable of hydrolyzing proteins that fall into the proteasome. All the genes encoding the proteins alpha-subunit appeared interchangeable, and most of the genes of the beta subunit was irreplaceable (Fig. 2). This protein-essential gene products interact Mezhuyev themselves. Scientists have tried to replace the yeast proteasome genes orthologous genes of other organisms in addition to humans. And, as in the case of human genes, foreign genes can replace the alpha subunit of the yeast proteasome, but could not replace the beta-subunit. It turns out that part of the proteasome were subjected to different selection pressures. Here again we can see the separation Feature: proteins that are involved in the hydrolysis proved indispensable, and the proteins that make up the entrance to the proteasome, can be replaced by the corresponding proteins of other organisms.
Fig. 2. Interchangeable (yellow) and essential (blue) in the composition of proteins of the proteasome. Left shows the interface between the two yeast proteins, one part of which can fulfill the human protein, although the amino acid sequences of the human and yeast embodiments coincide only halfway. In this case, the value has only a form of the protein. The image of the article under discussion in Science
Judging by the results of this work, if any genes begin to change, they prefer to do it in the company of close colleagues. Indeed, proteins involved in the same process, it is necessary to adapt to each other, so that the system as a whole remained working.
In addition to the fundamental interest (to understand how proteins are parted similar human and yeast), and work has important practical results. After all, by leaps and bounds, both in single-celled organisms that multiply rapidly, convenient to experiment. However, research on yeast is difficult to extrapolate that has the biggest practical importance – for human biology. Judging according to scientists, it is theoretically possible to obtain yeast strains with whole metabolic pathways consisting of human enzymes. In such "humanized" yeast is convenient to study human proteins and to test potential drugs.
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