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Crossbar switch
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In electronics and telecommunications, a crossbar switch (cross-point switch, matrix switch) is a collection of switches arranged in a matrix configuration. A crossbar switch has multiple input and output lines that form a crossed pattern of interconnecting lines between which a connection may be established by closing a switch located at each intersection, the elements of the matrix. Originally, a crossbar switch consisted literally of crossing metal bars that provided the input and output paths. Later implementations achieved the same switching topology in solid-state electronics. The crossbar switch is one of the principal telephone exchange architectures, together with a rotary switch, memory switch,[citation needed] and a crossover switch.
Crossbar telephone exchange of1903 for four subscribers (vertical bars), having four cross-bar talking circuits (horizontal bars), and one bar to connect the operator (T). The lowest cross-bar connects idle stations to ground to enable the signaling indicators (F). The switch is operated manually with metal pins that create a connection between the horizontally and vertically arranged bars.[1]
1 General properties
3 Implementations
3.1 Mechanical
3.2 Electromechanical switching in telephony
3.3 Instrumentation
3.4 Telephone exchange
3.5 Semiconductor
4 Arbitration
General propertiesEdit
A crossbar switch is an assembly of individual switches between a set of inputs and a set of outputs. The switches are arranged in a matrix. If the crossbar switch has M inputs and N outputs, then a crossbar has a matrix with M × N cross-points or places where connections can be made. At each crosspoint is a switch; when closed, it connects one of the inputs to one of the outputs. A given crossbar is a single layer, non-blocking switch. A crossbar switching system is also called a coordinate switching system.
Collections of crossbars can be used to implement multiple layer and blocking switches. A blocking switch prevents connecting more than one input. A non-blocking switch allows other concurrent connections from inputs to other outputs.
ApplicationsEdit
Crossbar switches are commonly used in information processing applications such as telephony and circuit switching, but they are also used in applications such as mechanical sorting machines.
The matrix layout of a crossbar switch is also used in some semiconductor memory devices which enables the data transmission. Here the bars are extremely thin metal wires, and the switches are fusible links. The fuses are blown or opened using high voltage and read using low voltage. Such devices are called programmable read-only memory.[2] At the 2008 NSTI Nanotechnology Conference a paper was presented that discussed a nanoscale crossbar implementation of an adding circuit used as an alternative to logic gates for computation.[3]
Matrix arrays are fundamental to modern flat-panel displays. Thin-film-transistor LCDs have a transistor at each crosspoint, so they could be considered to include a crossbar switch as part of their structure.
For video switching in home and professional theater applications, a crossbar switch (or a matrix switch, as it is more commonly called in this application) is used to distribute the output of multiple video appliances simultaneously to every monitor or every room throughout a building. In a typical installation, all the video sources are located on an equipment rack, and are connected as inputs to the matrix switch.
Where central control of the matrix is practical, a typical rack-mount matrix switch offers front-panel buttons to allow manual connection of inputs to outputs. An example of such a usage might be a sports bar, where numerous programs are displayed simultaneously. Ordinarily, a sports bar would install a separate desk top box for each display for which independent control is desired. The matrix switch enables the operator to route signals at will, so that only enough set top boxes are needed to cover the total number of unique programs to be viewed, while making it easier to control sound from any program in the overall sound system.
Such switches are used in high-end home theater applications. Video sources typically shared include set-top receivers or DVD changers; the same concept applies to audio. The outputs are wired to televisions in individual rooms. The matrix switch is controlled via an Ethernet or RS-232 connection by a whole-house automation controller, such as those made by AMX, Crestron, or Control4, which provides the user interface that enables the user in each room to select which appliance to watch. The actual user interface varies by system brand, and might include a combination of on-screen menus, touch-screens, and handheld remote controls. The system is necessary to enable the user to select the program they wish to watch from the same room they will watch it from, otherwise it would be necessary for them to walk to the equipment rack.
The special crossbar switches used in distributing satellite TV signals are called multiswitches.
ImplementationsEdit
Historically, a crossbar switch consisted of metal bars associated with each input and output, together with some means of controlling movable contacts at each cross-point. The first switches used metal pins or plugs to bridge a vertical and horizontal bar. In the later part of the 20th century, the use of mechanical crossbar switches declined and the term described any rectangular array of switches in general. Modern crossbar switches are usually implemented with semiconductor technology. An important emerging class of optical crossbars is implemented with microelectromechanical systems (MEMS) technology.
MechanicalEdit
A type of mid-19th-century telegraph exchange consisted of a grid of vertical and horizontal brass bars with a hole at each intersection (c.f. top picture). The operator inserted a metal pin to connect one telegraph line to another.
Electromechanical switching in telephonyEdit
A telephony crossbar switch is an electromechanical device for switching telephone calls. The first design of what is now called a crossbar switch was the Bell company Western Electric's coordinate selector of 1915. To save money on control systems, this system was organized on the stepping switch or selector principle rather than the link principle. It was little used in America, but the Televerket Swedish governmental agency manufactured its own design (the Gotthilf Betulander design from 1919, inspired by the Western Electric system), and used it in Sweden from 1926 until the digitization in the 1980s in small and medium-sized A204 model switches. The system design used in AT&T Corporation's 1XB crossbar exchanges, which entered revenue service from 1938, developed by Bell Telephone Labs, was inspired by the Swedish design but was based on the rediscovered link principle. In 1945, a similar design by Swedish Televerket was installed in Sweden, making it possible to increase the capacity of the A204 model switch. Delayed by the Second World War, several millions of urban 1XB lines were installed from the 1950s in the United States.
In 1950, the Ericsson Swedish company developed their own versions of the 1XB and A204 systems for the international market. In the early 1960s, the company's sales of crossbar switches exceeded those of their rotating 500-switching system, as measured in the number of lines. Crossbar switching quickly spread to the rest of the world, replacing most earlier designs like the Strowger (step-by-step) and Panel systems in larger installations in the U.S. Graduating from entirely electromechanical control on introduction, they were gradually elaborated to have full electronic control and a variety of calling features including short-code and speed-dialing. In the UK the Plessey Company produced a range of TXK crossbar exchanges, but their widespread rollout by the British Post Office began later than in other countries, and then was inhibited by the parallel development of TXE reed relay and electronic exchange systems, so they never achieved a large number of customer connections although they did find some success as tandem switch exchanges.
Crossbar switches use switching matrices made from a two-dimensional array of contacts arranged in an x-y format. These switching matrices are operated by a series of horizontal bars arranged over the contacts. Each such select bar can be rocked up or down by electromagnets to provide access to two levels of the matrix. A second set of vertical hold bars is set at right angles to the first (hence the name, "crossbar") and also operated by electromagnets. The select bars carry spring-loaded wire fingers that enable the hold bars to operate the contacts beneath the bars. When the select and then the hold electromagnets operate in sequence to move the bars, they trap one of the spring fingers to close the contacts beneath the point where two bars cross. This then makes the connection through the switch as part of setting up a calling path through the exchange. Once connected, the select magnet is then released so it can use its other fingers for other connections, while the hold magnet remains energized for the duration of the call to maintain the connection. The crossbar switching interface was referred to as the TXK or TXC (telephone exchange crossbar) switch in the UK.
Western Electric 100-point six-wire Type B crossbar switch
However, the Bell System Type B crossbar switch of the 1960s was made in the largest quantity. The majority were 200-point switches, with twenty verticals and ten levels of three wires, Each select bar carries ten fingers so that any of the ten circuits assigned to the ten verticals can connect to either of two levels. Five select bars, each able to rotate up or down, mean a choice of ten links to the next stage of switching. Each crosspoint in this particular model connected six wires. The vertical off-normal contacts next to the hold magnets are lined up along the bottom of the switch. They perform logic and memory functions, and the hold bar keeps them in the active position as long as the connection is up. The horizontal off-normals on the sides of the switch are activated by the horizontal bars when the butterfly magnets rotate them. This only happens while the connection is being set up, since the butterflies are only energized then.
Late-model Western Electric crossbar switch
Back of Type C
The majority of Bell System switches were made to connect three wires including the tip and ring of a balanced pair circuit and a sleeve lead for control. Many connected six wires, either for two distinct circuits or for a four wire circuit or other complex connection. The Bell System Type C miniature crossbar of the 1970s was similar, but the fingers projected forward from the back and the select bars held paddles to move them. The majority of type C had twelve levels; these were the less common ten level ones. The Northern Electric Minibar used in SP1 switch was similar but even smaller. The ITT Pentaconta Multiswitch of the same era had usually 22 verticals, 26 levels, and six to twelve wires. Ericsson crossbar switches sometimes had only five verticals.
InstrumentationEdit
For instrumentation use, James Cunningham, Son and Company[4] made high-speed, very-long-life crossbar switches[5] with physically small mechanical parts which permitted faster operation than telephone-type crossbar switches. Many of their switches had the mechanical Boolean AND function of telephony crossbar switches, but other models had individual relays (one coil per crosspoint) in matrix arrays, connecting the relay contacts to [x] and [y] buses. These latter types were equivalent to separate relays; there was no logical AND function built in. Cunningham crossbar switches had precious-metal contacts capable of handling millivolt signals.
Telephone exchangeEdit
Early crossbar exchanges were divided into an originating side and a terminating side, while the later and prominent Canadian and US SP1 switch and 5XB switch were not. When a user picked up the telephone handset, the resulting line loop operating the user's line relay caused the exchange to connect the user's telephone to an originating sender, which returned the user a dial tone. The sender then recorded the dialed digits and passed them to the originating marker, which selected an outgoing trunk and operated the various crossbar switch stages to connect the calling user to it. The originating marker then passed the trunk call completion requirements (type of pulsing, resistance of the trunk, etc.) and the called party's details to the sender and released. The sender then relayed this information to a terminating sender (which could be on either the same or a different exchange). This sender then used a terminating marker to connect the calling user, via the selected incoming trunk, to the called user, and caused the controlling relay set to send the ring signal to the called user's phone, and return ringing tone to the caller.
The crossbar switch itself was simple: exchange design moved all the logical decision-making to the common control elements, which were very reliable as relay sets. The design criteria specified only two hours of downtime for service every forty years, which was a large improvement over earlier electromechanical systems. The exchange design concept lent itself to incremental upgrades, as the control elements could be replaced separately from the call switching elements. The minimum size of a crossbar exchange was comparatively large, but in city areas with a large installed line capacity the whole exchange occupied less space than other exchange technologies of equivalent capacity. For this reason they were also typically the first switches to be replaced with digital systems, which were even smaller and more reliable.
Two principles of crossbar switching existed. An early method was based on the selector principle, which used crossbar switches to implement the same switching fabric used with Strowger switches. In this principle, each crossbar switch would receive one dialed digit, corresponding to one of several groups of switches or trunks. The switch would then find an idle switch or trunk among those selected and connect to it. Each crossbar switch could only handle one call at a time; thus, an exchange with a hundred 10×10 switches in five stages could only have twenty conversations in progress. Distributed control meant there was no common point of failure, but also meant that the setup stage lasted for the ten seconds or so the caller took to dial the required number. In control occupancy terms this comparatively long interval degrades the traffic capacity of a switch.[citation needed]
Bare-strip wiring of a 100-point six wire Type B Bell System switch
Starting with the 1XB switch, the later and more common method was based on the link principle, and used the switches as crosspoints. Each moving contact was multipled to the other contacts on the same level by bare-strip wiring, often nicknamed banjo wiring.[6] to a link on one of the inputs of a switch in the next stage. The switch could handle its portion of as many calls as it had levels or verticals. Thus an exchange with forty 10×10 switches in four stages could have one hundred conversations in progress. The link principle was more efficient, but required a complex control system to find idle links through the switching fabric.
This meant common control, as described above: all the digits were recorded, then passed to the common control equipment, the marker, to establish the call at all the separate switch stages simultaneously. A marker-controlled crossbar system had in the marker a highly vulnerable central control; this was invariably protected by having duplicate markers. The great advantage was that the control occupancy on the switches was of the order of one second or less, representing the operate and release lags of the X-then-Y armatures of the switches. The only downside of common control was the need to provide digit recorders enough to deal with the greatest forecast originating traffic level on the exchange.
The Plessey TXK1 or 5005 design used an intermediate form, in which a clear path was marked through the switching fabric by distributed logic, and then closed through all at once.
Crossbar exchanges remain in revenue service only in a few telephone networks. Preserved installations are maintained in museums, such as the Museum of Communications in Seattle, Washington, and the Science Museum in London.
SemiconductorEdit
Semiconductor implementations of crossbar switches typically consist of a set of input amplifiers or retimers connected to a series of interconnects within a semiconductor device. A similar set of interconnects are connected to output amplifiers or retimers. At each cross-point where the bars cross, a pass transistor is implemented which connects the bars. When the pass transistor is enabled, the input is connected to the output.
As computer technologies have improved, crossbar switches have found uses in systems such as the multistage interconnection networks that connect the various processing units in a uniform memory access parallel processor to the array of memory elements.
ArbitrationEdit
A standard problem in using crossbar switches is that of setting the crosspoints.[citation needed] In the classic telephony application of crossbars, the crosspoints are closed, and open as the telephone calls come and go. In Asynchronous Transfer Mode or packet switching applications, the crosspoints must be made and broken at each decision interval. In high-speed switches, the settings of all of the crosspoints must be determined and then set millions or billions of times per second. One approach for making these decisions quickly is through the use of a wavefront arbiter.
Matrix mixer
Nonblocking minimal spanning switch - describes how to combine crossbar switches into larger switches.
RF switch matrix
^ Kennedy, Rankin (1903 edition (five volumes) of pre-1903 four volume edition.) Electrical Installations, vol. V, London: Caxton
^ Chen, Yong; Jung, Gun-Young; Ohlberg, Douglas A. A.; Li, Xuema; Stewart, Duncan R.; Jeppesen, Jan O.; Nielsen, Kent A.; Stoddart, J. Fraser (2003). "Nanoscale molecular-switch crossbar circuits". Nanotechnology. 14 (4): 462–8. Bibcode:2003Nanot..14..462C. doi:10.1088/0957-4484/14/4/311.
^ Mouttet, B. (2008-06-02). "Logicless Computational Architectures with Nanoscale Crossbar Arrays". NSTI Nanotech 2008 Conference. Archived from the original on 2016-03-04. Retrieved 2008-06-02.
^ Hinrichs, Noël (1964). "6. The Era of Automation". The Pursuit of Excellence. James Cunningham, Son & Co.
^ Hinrichs 1964, Crossbar Switch
^ The Western Electric Engineer: Volumes 5-7. Western Electric. 1961. p. 23.
Pacific Telephone and Telegraph Company. General Administration Engineering Section (1956). Survey of telephone switching. San Francisco, California. OCLC 11376478.
Scudder, F.J.; Reynolds, J.N. (January 1939). "Crossbar Dial Telephone Switching System". Bell System Technical Journal. 8 (1): 76–118. doi:10.1109/EE.1939.6431910. S2CID 51659407. Retrieved 23 April 2015.
Images on an Ericsson ARF crossbar switch(in Dutch)
Retrieved from "https://en.wikipedia.org/w/index.php?title=Crossbar_switch&oldid=1130811833"


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Eng /
The original illustration to the
astronomy book of the french astronomer Flammarion.
1) A chemical compound known as dimethylether CH3?-O-CH3? or also as ethoxyethane, CH3?-CH2?-O-CH;2-CHt?;3.
2) A term commonly used to describe the medium of the radio.
3) Classically the element of the spirit.
Below the considerations about the classical definition.
A classical term for the medium of the spirit. According to the ancient Greeks was it the substance from which light emanated. In greek mythology the god Aether is the soul of the world. By vedic culture this is corroborated in the ether as being the sky which is also called akasha, the element that represents the first one of creation basic to the later ones in evolution of fire, water, earth and air. The Supreme Personality of Godhead in vedic theology may, according the bhâgavata purâna 11.5: 19 e.g., be considered the personification of the ether and as an element may it be regarded the representation of the supersoul, like with the Greeks. The Chinese, by name of the neo-confucianists, call the ether qi and consider it the basis for the generation of the creation and as that in which it also dissolves. To the way of the human virtues must according to them the troubling of the ether be cleared.
Modern physics in argument about it
In modern time, Einstein built his theory on the denial of the ether since it couldn't all that easy be proven by experiment. Thus he postulated his theory of constants, the so-called theory of relativity he himself preferred to name a 'theory of invariants'. A theory indeed, for something that is difficult to measure, might still exist; and that might thus be so with variations in the speed of light that are indicative of a fixed frame of reference like the ether. Ever since Einstein introduced his theory, have there been doubts among physicists whether the speed of light in empty space would be such an absolute constant. The ancient philosopher Herakleitos said that in principle everything is in flux (panta rhei) and the later french philosopher René Descartes stated that empty space does not exist, for according him all the cosmos is connected in force fields. Thus, looking at the stars keeping their place in the galaxy, it is difficult to deny the force field of the galaxy holding them together and possibly influencing the speed of light. Also may, as was proven by modern experiments, light travel faster, e.g. laser light under special circumstances. And so is, being serious about the evidence of the speed of light not always being constant, the stars moving around in the galaxy and the insight of possible and plausible new interpretations, of e.g. Maurizio Consoli, of the Michelson and Morely experiment to measure the ether, the existence of a fixed background by theory and experiment confirmed. That fixed background may indeed be described by the concept of the ether or the effect of the electromagnetic force field of our galaxy. In other words leads this theoretical position to the idea that the ether is our life, that the conditioning to the ether, through the cyclic of time connected with it, specifically is formative to our our spiritual as wel as our material life. We therefrom speak of the ether when we relate to that force field and experience our mind in that sphere as the 'sound in the ether ', as the classical hindu-scripture the Bhagavad Gîtâ confirms. The mind, thus seen, springs from the ether in our being identified with the cyclic of the timing of our material actions and finds at the other hand its peace again with the meditative expansion of us souls detaching on the primordial ether of spacetime.
Even though Einstein on the basis of the absolute of the speed of light and his special theory of relativity is presented as being the source for the refutation of the existence of the ether as a material element, must the case be considered differently. Einstein later on in 1920 returned to the subject of the ether when he described it with according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. His idea of the ether as being space with characteristics of gravity, is relativistic as opposed to that of H. Lorentz who departed more from an absolute concept of time with the ether. Einstein's insight led to the notion of the existence of different forms of ether which historically can be traced back to the three forms of Vishnu, knowing Garbo- Kâranao-and Kshirodakas'âi Vishnu (Satvata Tantra), which to themselves constitute the three representations of the ether of timespace, galactic space and the curved space of material objects as planets and stars. The first, the ether of timespace, is expansive and linear, the second, the galactic, is contracting, cyclic and creative, and is known as the 'Creator', 'Something' or the Force' and the third one, the planetary or local ether, is electromagnetically determined by the characteristics of the object in space and is also known as the radio-ether. The insight of Lorentz concerning the true time of cyclic nature with the ether is of assistance in confirming the filognostic thesis that says that when the time of the clock is equal to the true time of nature, the instability of the experience of time or psychological time then is terminated (see also the definition of Time). Thus served Einstein and Lorentz filognostically not each others refutation, but served the two rather the support of filognostically commensurate arguments. What does perish in this debate though is the notion of the constancy of light speed in a vacuum.
Filognosy and the ether
So must filognostically, viz. loving the knowledge, be said: the ether as the effect of the force field of the galaxy, which constitutes a fixed background which might be influencing the speed of light, does exist on classical grounds as well as on the ground of reason and logic, the observation of the order of the stars spinning in the galaxy (the universal ether), the red shift of the spectrum of galaxies (the primal ether), and the gravitational lenses around stars (the local ether); an exitence confirmed by the description of Einstein and the interpretations of the experiments done. Thus constitutes the ether, in its relation to cyclic time, a viable paradigm. This paradigm is defended at this site, as the unifying idea of the combined cyclic of natural time, the expansion of space-time and the stable self-awareness of having a soul of balance - or witness of the time - therewith, which as a paradigm scientifically, spiritually and personally correctly respected, as well offers room to the classical philosophy and theology, as also to the analytical, artistic and spiritual association, as also a to-the-point empirical perceiving, theorizing and experimenting in a mechanistic sense. In fact are the two seemingly contradictory departments of our cultures united when we, with the assumption of a filognostical, or syncretic form of spirituality free from speculations, are no longer denying the existence of the ether.
The concept of ether as known from the classics implies a new paradigm of culture for the twenty-first century which states that, after the geocentric paradigm of Ptolemy and the heliocentric way of thinking we entertained ever since with Galileo Galilei, there is the order of life and thought as derived from the galactocentric relating to the fixed background of the forcefield of the planet and the star, the galaxy of our universe, and all the galaxies of the cosmos that together constitute the reality of the one, but divided ether, the Force so to say. It is for this reason that the Hindus speak of the mountain Meru on which the creator Brahmâ resides in the center of the universe. Ever since we photographed this mountain of stars in the middle of the galaxy heaping about the black hole in the center at Sagittarius A, is the bhâgavata purâna 5.16: 7, speaking about it as stretching upwards as far as downwards, not that allegorical anymore.
Implications; the policy
Accepting the full reality of the ether, as it always was respected in spiritual and religious exercises to the cyclic of time, must, wishing such practically as a common notion of civil order and sober culture, in the meditations on the cosmic expansion of space-time with it, the ether be kept in mind as a stable time-base for e.g. a cakra-calendar, with, next to the respect for the order of the sun and the moon, e.g. birthdays celebrated in respect of the precession of the equinox, the drift of the stars in the galaxy who are every year about twenty minutes further up in the calendar, or with a special day set to the galaxy center in remembering the day when we are closest to the point of spin: a galactic new year (at 2000, O hr 6-7 July). The ether as a stable basis of time also leads to the notion of 1) a tempometer as an improvement to the standardtime clocks, and 2) a deregulation of those legal settlements of time that defy the natural order of cyclic time. Thus seen in the culture and thus furthermore also reflected in the educational system, is the concept of the ether of relevance to the personal and collective integrity of the scientific, spiritual, religious and thus also political interest of a truthful strategy of cultural maintenance and order of relating to the forces of nature, we at this site have baptized with the name filognosy: the straight love of knowledge in cultural comprehension.
Ether: de nederlandse pagina hierover.
Galactic year
Galactic time - main-article
Cakra-order
The Ether Exists! Read the introductions and the synopsis together making for the book The Ether Exists!.
Ether-wikipedia
Luminiferous ether-Wikipedia
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Home » Microbiology » Cell Biology » Chromosome Definition, Function, Structure, Types
Chromosome Definition, Function, Structure, Types
Chromosomes are a collection of tightly coiled DNA that are located in the nucleus of virtually every cell of our body. Humans possess 23 chromosome pairs.
Features of eukaryotic chromosome
Size of Chromosome
Shape of Chromosome
Chemical composition of chromosome
Duplication of Chromosome
Chromosomes and cell division
Chromosomes and Protein Production
Mutation of Chromosome
Types of Chromosomes
Prokaryotic Chromosomes
Eukaryotic Chromosome
Differences Between Eukaryotic Chromosome and Prokaryotic Chromosomes
Models Proposed for Chromosome Structure
Function of Chromosomes
Number of chromosomes of different eukaryotes
The term chromosome originates from the Greek chroma, which means "colour" and"soma", and "body" which refers to the strong staining they get from certain dyes.
The term was invented by the German Anatomist Heinrich Wilhelm Waldeyer, referring to the term chromatin which was invented by Walther Flemming, who was the first to discover the process of cell division.
Certain of the earlier words in karyology have been deemed obsolete. For instance, Chromatin (Flemming 1880) and Chromosom (Waldeyer 1888) Both attribute the color of a state that is not colored.
In animal and plant cells DNA is tightly packed into thread-like structures, referred to as"chromosomes. This is different from bacteria, where DNA is floating freely within the cell.
One length of DNA is wrapped multiple times over a variety of proteins, known as histones to create structures known as nucleosomes.
These nucleosomes then wrap tightly to form loops of chromatin.
The chromatin loops are connected to create a complete chromosome.
Every chromosome has two arms that are short (p arms) as well as two more long arms (q arms) and a centromere that holds the entire thing together in the center.
Humans have 23 pairs chromosomes (46 in all) One set comes from your mother while another set is from your father.
Of the 23 pairs, only one pair is a sex chromosome, meaning that they will differ in the case of gender-neutral or female (XX for females as well as XY for males).
The remaining 22 pair are called autosomes (non-sex chromosomes) and are the same for females and males.
The DNA that makes up every chromosome in our bodies is made up of many thousands of genes.
The ends of each chromosome are DNA fragments known as Telomeres. Telomeres shield the ends of chromosomes when DNA replication occurs by forming an elongated cap, similar to the tip of a plastic shoelace.
The majority of eukaryotic DNA chromosomes have packaging proteins known as histones that are assisted by chaperone proteins, connect to and expand the DNA molecule, ensuring its integrity. The chromosomes exhibit a complex three-dimensional structurethat plays an important part in the regulation of transcription.
Chromosomes appear under a microscope light only during the metaphase phase of the cell's division (where all chromosomes are aligned to the middle of the cell , in their compressed version). In the beginning every chromosome is duplicated (S phase) and each copy is joined by an X-shaped centromere. This results in an shape-like structure called an X (pictured above) depending on whether the centromere is located in equatorially or in an arm-like structure when the centromere is situated further distally. The copies that are joined are known as sister chromatids.
In metaphase, the X-shaped structure is referred to as a metaphase chromosome. This is highly condensed , making it easier to identify and examine.
In animals, chromosomes achieve their maximum compaction in anaphase in chromosome segregation.
Chromosomal meiosis and later sexual reproduction plays a major part in the genetic diversity. In the event that these structure are controlled in a way that is not correct, such as chromosomal instability or translocation the cell could suffer a mitotic catastrophe. This will usually cause cells undergo apoptosis, leading to the death of the cell however, sometimes mutations within cells can block the process and cause the growth of cancer.
Certain people use the term chromosome in a broad sense to refer to the unique parts of chromatin found in cells, which are visible or not when using light microscope. Some use the term in a narrower sense to mean the distinct parts of chromatin that occur in cell division that are visible with light microscopes because of high condensation.
Illustration showing how DNA is packaged into a chromosome. | Image credit: Genome Research Limited
Chromosomes are most visible in metaphase.
Chromosomes carry the genes in a linear way.
Chromosomes can vary in size, shape and the number of them in different species of animals and plants.
Chromosomes possess the property of self-duplication and mutation.
Chromosomes consist comprised of DNA,RNA and proteins.
The size of chromosomes is measured in mitotic metaphase, usually measured in length and dia
The Chromosome of plants is usually longer than animals.
Plant Chromosomes typically measure 0.8-7um in length, whereas animals' chromosomes range from 0.5-4um in length.
Chromosomes ' size vary between species
The shape of the chromosome is typically determined by the location of the centromere.
The chromosomes typically exit in three different forms such as. rod shape, V shape, and J shape.
Structurally , chromosomes consist of seven components
Diagram of a replicated and condensed metaphase eukaryotic chromosome. (1) Chromatid – one of the two identical parts of the chromosome after S phase. (2) Centromere – the point where the two chromatids touch. (3) Short arm (p). (4) Long arm (q). | Image Source: https://en.wikipedia.org/wiki/File:Chromosome.svg
Centromere: It's an area of the chromosome to which spindle fibers are connected. This is known as primary constriction or centromere or Kinetochore.
Chromatid: One of two distinct longitudinal subunits that make up the chromosome, is known as chromatid. Chromatids come in two varieties: sister chromatids as well as non sister chromatids.
Secondary constriction: Certain chromosomes has secondary constriction along with primary constriction. The chromosomal region that lies between telomeres is known as a trapant or satellite. The chromosome that has satellites is referred to"satellite chromosome.
Telomere: Telomeres are the two sides of a the chromosome are referred to as Telomeres. Telomeres are extremely stable and do not connect or join with telomeres of the other chromosome.
Chromomere: The chromosomes in certain species have tiny beads-like structures known as Chromomeres. The chromomere structure in the chromosome remains always the same.
Chromonema: Threadlike coils found in chromosomes and chromatids are referred to as the chromonema (plural the term chromonemata).
Matrix: It's an element of fluid that contains chromonemata. It is referred to as matrix.
Chemically chromosomes are nucleoproteins, which in nature, which means they are made up of DNA, RNA and protein. In general, chromosomes have 30-40 50% DNA, 50-65 percent protein, and 0.5to 10 percent DNA
There is a lot of DNA that is present in the somatic cells is constant. The DNA content of gametic cells is about half the somatic cell. The DNA in chromosomes are comprised of two kinds: i) Unique DNA and ii) Repetitive DNA
Unique DNA: unique DNA is made up of the DNA sequences that exist in only one DNA copy and are unique in the world of. It is referred to as non-repetitive DNA. Codes for proteins that must be present huge quantities for the cell. eg- storage protein.
Repetitive DNA: Repetitive DNA comprises DNA nucleotides or base sequences that can be as little as a few hundred bases (bp) long and comprised of up millions of copies within a genome. Human genome contains 30% repetitive DNA. Repetitive DNA can further be divided into
Highly repetitive DNA, and
Moderately repetitive DNA
Purified chromatin contain 10-15% RNA. The chromosome-associated RNA comprises messenger transcript RNA, transfer RNA as well as the ribosomal RNA.
The chromosome-associated protein is divided into two broad categories;
Histone or the protein of base
Non-histone proteins (Non histone protein) is acidic. histone proteins are fundamental in nature due to basic amino acids)
i) Histone protein
histones comprise around 80% of overall chromosomal proteins. They're found in a close proportion to DNA. Five histone fractions are present, including 1H1, 2H2a and 2H2b, 2H3 , and 2H4.
ii) Non histone protein
Non histone proteins constitute up 20 percent of entire protein weight. The composition of non histone protein differs from species to species. Non histone protein is comprised of several important enzymes such as DNA and RNA polymerase.
Within a cell DNA doesn't usually exist on its own, however, it's a part of specific proteins that help organize it and provide it with shape. In eukaryotes they have proteins that include the histones. They are a collection of base (positively chargeable) proteins that create "bobbins" around DNA, which negatively charged DNA could be wrapped. Apart from organizing DNA, and making it less bulky histones play an essential function in determining which genes are in active. The combination of DNA with histones and structural proteins is known as Chromin.
In the majority of the time in the cells, chromatin becomes decondensed. It is found in thin, long strings that appear like tiny squiggles in the microscope. In this condition, DNA is accessed quickly by cell machines (such in the form of proteins which can read and replicate DNA) and is crucial for allowing cells to develop and function.
Decondensed might seem like an odd name for this kind of state but why not just label it "stringy"? However, it makes sense once you realize that chromatin also has the ability to condense. Condensation occurs as cells are nearing the point of division. When chromatin is condensed it is clear that the DNA of eukaryotic cells is not only one long string. It's actually broken into distinct linear pieces, referred to as the chromosomes. Bacteria also have chromosomes but their chromosomes tend to be circular.
Chromatin | Image Source: https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/cell-cycle/a/dna-and-chromosomes-article
Chromosome duplication happens before the division process of mitosis as well as meiosis. DNA replication processes permit the correct chromosome number to be maintained after the original cell splits. A duplicated chromosome comprises by two identical chromosomes, referred to as sister chromatids, which are linked to the center of the centromere. Sister chromatids stay together until the conclusion in the process of division, when the spindle fibers separate them, and then encased inside separate cells. After the paired chromatids are separated and are separated from each other it is the case that each is called an chromosome daughter.
One of the key aspects of effective cell division involves the right distribution of the chromosomes. When mitosis is occurring, this implies that chromosomes need to be divided between two cells. In meiosis, the chromosomes have to be split between four cells. The cell's spindle apparatus the one responsible for shifting chromosomes in cell division. This kind of cell movement results from interaction between microtubules of the spindle as well as motor proteins, which work in tandem to control and separate the chromosomes.
It is crucial that the correct amount of chromosomes is maintained within cells that divide. Incorrect cell division could cause people to have imbalanced number of chromosomes. The cells could have too many or too few chromosomes. This kind of situation can be referred to as aneuploidy. It can occur in the autosomal chromosomes that occur during mitosis, or in sex chromosomes that are formed during meiosis. Aneuploidies in chromosomes could cause birth problems, developmental disabilities, and even death.
Protein production is an essential cell function that depends on DNA and chromosomes. Proteins are essential molecules that are essential to perform a variety of functions of the cell. Chromosomal DNA has segments that are genes that encode for proteins. When proteins are produced the DNA is unwinded along with its codifying segments. These segments are translated into an transcript of RNA. The DNA information is then transferred from the nucleus, and later transformed into proteins. Ribosomes as well as another DNA molecule, referred to as transfer RNA, collaborate to connect to the transcript of RNA and transform the encoded message into proteins.
Chromosome changes are the modifications that occur on the chromosomes. They are usually due to either errors that occur during meiosis or exposure to mutagens like radiation or chemicals. Chromosome breakage or duplications may result in a variety of structural changes in chromosomes which tend to be harmful to the person. These kinds of mutations cause some chromosomes that have additional genes, insufficient genes, or those that are located in the wrong sequence. Mutations can also result in cells with abnormal amounts of the chromosomes. The abnormal chromosome number usually occurs due to disjunction, or failure of homologous chromosomes correctly during meiosis.
Types of Chromosomes Based on the Location of Centromere
1. Metacentric Chromosomes
Metacentric chromosomes include the centromere located in the middle which means that each section is of equal length. Human chromosomes 3 and 1 are both metacentric.
2. Submetacentric Chromosomes
Submetacentric chromosomes are those with the centromere that is slightly offset from its center, leading to an asymmetry of both sections' lengths. Human chromosomes 4 to 12 are submetacentric.
3. Acrocentric Chromosomes
Acrocentric chromosomes possess one centromere, which is off from the center, which results in a very long and a extremely short segment. Human chromosomes 13,15 21 and 22 are Acrocentric.
4. Telocentric Chromosomes
Telocentric chromosomes contain the centromere located at the at the end of the genome. Humans don't have Telocentric chromosomes however they can be present in other species, like mice.
Types of Chromosomes Based on the Number of Centromeres
Based on the number of Centromeres the chromosomes are divided into five groups as;
Monocentric: Monocentricchromosomes are those that have just one centromere.
Dicentric: Dicentric chromosomes contain two centromeres.
Polycentric: Polycentricchromosomes include at least two centromeres
Acentric: They lack a centromeres. These chromosomes are freshly broken chromosomes that don't last long.
Non-located or Diffused: Diffused or non-located chromosomes have an indistinct centromeres spread across the length of the chromosome.
Chromosomes can also be classified into two categories , such as
Chromosomes for sexual chromosomes
Autosome
An autosome is a type of chromosome that isn't one of the sex chromosomes. The autosome members in a pair within diploid cells share similar morphologies, but differ from the allosomes that might differ in structure. The DNA found in autosomes is collectively referred to in the form of atDNA also known as auDNA.
For instance, humans are a diploid species with a genome that typically has the autosomes of 22 pair as well as an allosome pairing (46 chromosomes in total). The autosome pairs are identified by numerals (1-22 for human beings) roughly in the order of their size in base pairs, whereas allosomes are identified by their initials. In contrast, the allosome pair is composed of two X-chromosomes in females, or one X as well as one Y chromosome for males. Strange combinations of XYY various XXY and XXXXXX in addition to others Salome variations, are widely known to happen and often result in developmental anomalies.
Autosomes are still populated with sexuality-related genes, even though they're not sex-chromosomes. For instance the SRY gene located on the Y genome encodes the transcription factor TDF and is essential in determining male sex throughout the development. TDF acts by activating the SOX9 gene on chromosome 17 and mutations in the SOX9 gene may cause human beings with a normal Y chromosome to become females.
autosomal recessive gene | Image Source: https://en.wikipedia.org/wiki/Autosome#/media/File:Autosomal_recessive_inheritance.gif
Autosomes from all human species have been identified and mapped using the chromosomes of cells caught in metaphase or in prometaphase, and staining them using a particular dye (most frequently, Giemsa). These chromosomes can be usually regarded as karyograms for simple comparison. Geneticists in clinical research can compare the karyograms of an individual with a reference karyogram in order to identify the cytogenetic causes of specific characteristics. For instance the karyograms of someone who suffers from Patau Syndrome could reveal that they have three copies of the 13th chromosome. Karyograms and staining techniques can only detect large-scale disruptions to chromosomes–chromosomal aberrations smaller than a few million base pairs generally cannot be seen on a karyogram.
Sex chromosome
A sexchromosome (also known as an allosome, heterotypical or heterotypical chromosome or heterochromosome) or an idiochromosome) is a chromosome which is distinct from the normal autosome with regard to form size, shape, and behavior. Human sex chromosomes comprise a typical pair of mammal's allosomes determine the gender of an individual who is created through sexual reproduction. Autosomes are different from allosomes in that autosomes are found in pairs where members have the same structure however they different from the other pair within an allopolyploid cell. In contrast, individuals of an pairing might vary from the other and determine the sex.
Nettie Stevens, and Edmund Beecher Wilson both independently discovered sex chromosomes around 1905. But, Stevens is credited for finding these prior to Wilson.
The prokaryote genome is typically comprised of one chromosome and plasmids.
Eukaryota have more chromosomes. We can distinguish two kinds of eukaryota's mitochondrial kind of chromosomes (nuclear as well as mitochondrial) and, sometimes, even plasma plasmids.
Prokaryotic chromosomes can be found in the nucleoid of prokaryotic cells and are circular in shape.
Contrary to eukaryotic cells cell do not possess a nucleus that is membrane-bound. Instead their genetic material can be found in a portion in the cytoplasm, known as the nucleoid.
A prokaryotic cells typically is composed of a single circular chromosome that is coiled. There are however some prokaryotes with more than one. Vibrio cholerae, the bacterium responsible for the cholera outbreak has two circular chromosomes.
Every chromosome is home to DNA molecules that is supercoiled and compressed by nucleoid-associated protein (NAPs).
Prokaryotic cells could have only one chromosome. However, the chromosome that is one is a long DNA molecule that has to be compacted to fit in the tiny space. In a cell that is eukaryotic, DNA wraps around clusters histone proteins. But, the majority of prokaryotic cells aren't using histones to aid in storage of DNA. (Some Archaea do, but they're the exception instead of the norm.)
Similar to eukaryotic DNA and prokaryotic DNA is subjected to supercoiling but it's not wrapped around histone clusters before. Supercoiling employs the use of tension to bend a DNA molecule and wrap it around itself and creates loops.
Folding of DNA in prokaryotic cells is made easier by nucleoid-associated protein (NAPs) rather than histones. NAPs are proteins found within the nucleoid, which can attach to DNA molecules by causing folds and bends and are associated in processes like transcription and replication of DNA.
The Prokaryotic cell is haploid that is, they don't possess homologous chromosomes. pairs.
The majority of prokaryotic cells only have one chromosome. They have been classified as having haploid cell (1n with no the chromosomes that are paired). However, in Vibrio Cholerae, which has two chromosomes, they are distinct from each other. They are not homologous since they do not have identical genes at the same places.
Prokaryotes, like bacteria, reproduce through binary fission. This is an method of sexual reproduction that is comparable in the end result to mitosis, where two daughter cells are created and each has the same number of chromosomes that the parent cell. When bacteria undergo binary fissions, no mitotic spindle develops. Furthermore reproduction of the cell's genome is possible during the fission process.
Prokaryotic cells also contain small DNA molecules called plasmids.
Plasmids are tiny, circular DNA molecules that carry the cell's essential genes. Though plasmids come in a range of dimensions (ranging from a few thousand base pairs up to several hundred thousand) They typically contain a handful of genes. Resistance to antibiotics is a characteristic that is usually attributable to plasmid genes.
The genetic material in plasmids is distinct from the cell's main chromosome and they can reproduce independently of the chromosome. If a prokaryotic cell that has an plasmid divides, daughters cells each get an identical copy of the plasmid and its regular chromosome.
Eukaryotic chromosomes can be found within the nucleus of cells.
The main characteristic that differentiates the eukaryotic from the prokaryotic cells is that it has the membrane-bound nucleus.
The nucleus is the "control central" within the cells. It holds all the cells' genetic information known as DNA. Its nuclear membrane also known as the nuclear envelope, has pores, or channels that regulate molecular movement inside and out of the nucleus.
The DNA in the nucleus is organised into chromosomes.
In the simplest sense the chromosome is a DNA-based molecule which is tightly wrapped around proteins known as histones. Eukaryotic cells contain many chromosomes that are linear in their shape.
Each chromosome has an atom of DNA which is tightly wrapped around histone protein clusters.
DNA molecules are incredibly large, containing million of base pairs (matched nucleotides) each. What is the process that cells use to store these huge and bulky molecules? Like you would put thread or yarn on a spool. DNA is compressed in a coiled form, then folded into a compact size.
As a eukaryotic cell divides, each chromosome copies creating the identical twin chromatids that are joined together in length, with the strongest link through the centrromere.
The majority of eukaryotic cells have several linear chromosomes. However, prokaryotic cells possess only one circular chromosome.
Eukaryotic chromosomes reside in the nucleus, while prokaryotic chromosomes reside within the nucleoid.
In eukaryotic chromosomes DNA is wrapped around proteins called histones, and later, it's further compacted through the process of supercoiling as well as folding. In prokaryotic chromosomes DNA is supercoiled and pressed with nucleoid proteins.
Prokaryotic Chromosome
Shape Linear Circular
Number Multiple Single
Location Nucleus Nucleoid (region in cytoplasm)
Storage proteins Histones Nucleoid-associated proteins
The following paragraphs outline the top four models that have been proposed to model chromosome structure. The models are: 1. Molecular Model 2. Multi-Stranded Model or Polyneme Chromosome Model 3. General Chromosome Model 4. Folded Fibre Model.
1. Molecular Model
The model of chromosome structure was developed by Taylor and his coworkers in 1957 in 1963. It is built on the semiconservative replication of the eukaryotic chromosome. According to this model the chromatid is comprised of one DNA chain, with numerous DNA double helices are joined end-to-end with proteins.
Protein molecules' interactions with each other result in coiling and uncoiling of chromosomes. DNA molecules is broken by deoxyribonucleases however not by proteolytic enzymes.
2. Multi-Stranded Model or Polyneme Chromosome Model
This theory was first proposed by Ris in the year 1961, and by Ris along with Chandler after 1963. Based on this model, the chromosome has multi-stranded DNA, i.e. it has numerous DNA double helices, which are placed in a parallel fashion to one another. Each chromosome is separated into two chromatids. Each chromatid is composed up of 2 "half of chromatids" as well as each half-chromatid is made up from two "quarter quarter chromatids."
Every "quarter of a chromatid" is comprised of four chromatin fibers and each fibre of chromatin has 2 DNA double helices. The size of the double DNA helix is about 2 nanometers as well as two DNA molecules join with proteins to form the chromatin fiber.
The dimensions of chromatin fibres quarter chromatids and half chromatids and chromatids range from 10 nm 40 nm 40 nm 80 num, and 160 nm according to. So, each chromatid is comprised of 32 DNA molecules, whereas the metaphase chromosome has 64 DNA molecules. But, according to recent research the chromosome is not multi-stranded.
3. General Chromosome Model
The idea was put forward by Crick in 1971. It implies that DNA in the chromatid is a huge monomer that flows all the way between one side and another. The interband and bands of the chromosomes (especially gigantic chromosomes) are thought to serve different purposes. The bands are populated with global control DNA, whereas the inter-bands are filled with the fibrous DNA that codes for proteins.
4. Folded Fibre Model
DuPraw in the year 1965 developed this model based on of studies using electron microscopy of the human chromosomes. Based on this model, every chromatid is composed of a single long nucleoprotein complex (Chromatin fibers) with one DNA double helix is the primary arrangement of the axis. The chromosome model is widely accepted.
The most important characteristics that this model has are:
Prior to interphase replication, every chromosome is made up of one chromatid composed of one 500-200 A thick chromatin fibre every fibre has a large DNA double-helix, which is linked to proteins as well as RNA.
The chromatin fiber (chromatid) reproduces in the S phase of the call cycle to produce two sister chromatids , which are held together by non-replicated regions.
The sister chromatids are folded together to form a clear chromosome in prophase. sister chromatids remain joined by tiny un-replicated regions.
Specific folding patterns as well as packing pattern of chromatids from various chromosomes is believed to differ in certain ways. Therefore, each metaphase chromatid comprised of a tightly folded one chromatin fiber that ranges from 200 to 500 A diameter. The exact 3-dimensional structure of the nucleoprotein fibre within each chromatid isn't the same. This configuration changes from interphase to metaphase.
It can also be different from the same chromosome through meiosis and mitosis, in mature sperm, and also from the metaphase phase to the metaphase. The non-homologous chromosomes vary not just in their genetic content , but as well in their 3-dimensional layouts.
The model suggests that, in the region of the centromeric the chromatin fibres are continuous and move between one arm and another for every sister chromatid. the sister chromatids stay tightly together in this region until the point of their separation in anaphase. The model also suggests that some DNA is synthesized before sister chromatids split. The diagrammatic illustration of the model with folded fibres is shown in Fig. 8.2.
The chromatin fibers are thought to be composed of "A" or "B" types. The type A fibre lies in between the DNA double helix extended as well as the B type fully packed fibre. The DNA double helix measures approximately 20 A in diameter. It joins with histones to create nucleohistone fibrils.
The fibril is folded into super-helix with 100 A diameter and 120 A This is the kind of A fiber. The 100 A fiber folds due to the divalent effects of cations (Ca2+ Mg2+, Ca2+) in order to form an elongated system consisting comprising 250 A fibers.
The fibre that is packed fully is between 200 and 500 A in size. It is referred to as a B type fibre. When Mg2+ and Ca2++ are eliminated The 200-500 A fibers expand to form 100 A-fibrils. The process of digestion of the 100 A fibrils is accomplished by enzymes called proteinase. This results in an unidirectional 20-30 A thick stand (DNA double Helix) which is susceptible DNAase.
First time ever, Sutton as well as Bover suggested the importance of chromosomes for the process of heredity in 1902.
The primary purpose of chromosomes is to carry the most fundamental genetic material called DNA. DNA contains genetic information for many cell functions. These functions are crucial to the survival, growth and reproduction of organisms.
Histones and other proteins protect the Chromosomes. They protect them from damage caused by chemical (e.g. enzymes) as well as physical force. Therefore, chromosomes perform the role of protecting gene material (DNA) from harm in the course that is cell division.
Humans are blessed with 23 pairs of chromosomes of one of which is the sexchromosome. Females have two X-chromosomes while males have just one the Y and X chromosomes. The gender for the baby is determined by the number of chromosomes carried down by male. If X chromosomes are passed through XY, it will become female. If the Y chromosome is passed, a male develops.
In the course of cell division the spindle fibers connected to centromeres expand and serve a vital role. The contraction of the centromeres of the chromosomes assures a an exact dispersal of DNA (genetic material) to the nuclei of the daughter.
The chromosomes regulate how proteins are that are formed within our bodies and keep the order of DNA. The proteins are stored inside the coiled structure the chromosomes. The proteins that are bound to DNA aid in the proper packing of DNA.
Chromosomes ensure the success of division of cells throughout dieosis. The chromosomes of parent cells make sure that the right information is passed to daughter cells needed by the cell in order to grow and develop in a correct manner.
Chromosomes contain both histone as well as non-histone protein. these proteins regulate gene action. Cellular proteins that regulate genes function in a way by activating and deactivating the proteins. The process of activation and deactivation can either will expand or expand the chromosome.
Chromosomes contain the genetic material needed by the organism in order to grow and develop. DNA molecules are comprised from a series of units known as genes. Genes are the parts of DNA that encode for the specific proteins needed by cells for their optimal functioning.
Diploid number of chromosomes (2n)
Humans 23 46
Earthworm 18 36
Dogs 39 78
Lily 12 24
Frog 13 26
Turkey 41 82
Shrimp 127 254
Chimpanzee 24 48
(Solanum tuberosum) 24 48
Hare 24 48
(Danio rerio) 25 50
Water buffalo (Riverine type) (Bubalus bubalis) 25 50
Striped skunk(Mephitis mephitis) 25 50
(Ananas comosus) 25 50
(Giraffa camelopardalis) 15 30
(Pistacia vera) 15 30
(Helianthus annuus) 17 34
(Erethizon dorsatum) 17 34
(Arachis hypogaea) 20 40
American beaver
(Castor canadensis) 20 40
(Triticum aestivum) 21 42
(Macaca mulatta) 21 42
(Rattus norvegicus) 21 42
(Avena sativa) 21 42
(Ailuropoda melanoleuca) 21 42
(Fragaria × ananassa) 28 56
(Elephantidae) 28 56
(Capra hircus) 30 60
(Equus asinus) 31 62
(Cavia porcellus) 32 64
(Equus caballus) 32 64
Sloth bear
(Melursus ursinus) 37 74
(Ursus maritimus) 37 74
(Columbidae) 39 78
(Gallus gallus domesticus) 39 78
(Saccharum officinarum) 40 80
Crucian carp
(Carassius carassius) 50 100
Kamraj (fern)
(Helminthostachys zeylanica) 47 94
Rattlesnake fern
(Botrypus virginianus) 92 184
Black mulberry
(Morus nigra) 154 308 (highest amongst plants)
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https://en.wikipedia.org/wiki/Autosome
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Nucleoid Definition, Functions, Characteristics
Chromosome Abnormalities Types, Mechanism, Detection
MN Editors. (March 1, 2022).Chromosome Definition, Function, Structure, Types. Retrieved from https://microbiologynote.com/chromosome/
MN Editors. "Chromosome Definition, Function, Structure, Types." Microbiology Note, Microbiologynote.com, March 1, 2022.
Genetic Code – Definition, Characteristics, Wobble Hypothesis
Cell Growth – Definition, Types, Mechanisms
Parthenogenesis – Definition, Types
Fertilization – Definition, Types, Process
Gametogenesis – Definition, Steps
Meiosis – Definition, Types, Steps


TWO Conservative councillors have resigned.
Paul and Diana Brierley have stepped down with immediate effect, meaning all three Bradshaw seats will be up for grabs in the local elections in May, as Cllr Walter Hall's seat is also up for election.
Mr Brierley, who became a councillor in 2002, said he was finding it increasingly difficult to balance his council duties with his full-time job as a quantity surveyor.
Conservative Group Leader Cllr John Walsh said: "I know that for some time it has become increasingly difficult for Paul to combine his work with those of being a councillor.
"His job takes him away from Bolton during the working week and I know he has been concerned that it was not possible to carry out his duties as he would have wished.
It is understood the Brierleys are looking to move to Bristol.
Mrs Brierley said: "It has been an honour to serve the residents of Bradshaw ward.
Mr Brierley added: "It is increasingly difficult to maintain a full-time job and carry out the work as a councillor in the manner I would wish.


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Uber sells its self-driving vehicles arm
A self-driving Uber car makes its way down River Road in Pittsburgh.
(Gene J. Puskar / Associated Press)
By Bloomberg
Uber Technologies Inc. sold its self-driving-car division to Aurora Innovation Inc. and took a stake in the startup, creating a larger competitor to the leader in the field, Alphabet Inc.'s Waymo.
The deal will value Aurora at $10 billion, according to people familiar with the discussions who asked not to be identified discussing private information. In exchange for investing $400 million in Aurora, Uber will get a 26% ownership stake in the company. That number increases to 40% when counting the stakes held by the employees and investors of Uber's autonomous driving division. Uber Chief Executive Officer Dara Khosrowshahi and one other yet-to-be-named person representing Uber will join Aurora's board.
The deal, expected to close during the first quarter, also guarantees that when Aurora releases its self-driving vehicles, they'll launch on Uber's network.
By adding Uber's self-driving-car unit, Aurora will gain hundreds of engineers and access to one of the world's largest ride-hailing networks. For Uber, which has slashed high-profile cash-burning initiatives this year in a push to turn a profit in 2021, the deal will give it a significant stake in one of Silicon Valley's most promising autonomous driving startups.
Uber's driverless-car unit, Advanced Technologies Group, is a subsidiary, created just before Uber went public last year with its own $7.25-billion valuation. Still, the project's long time frame and high costs concerned Uber's investors SoftBank Group Corp., Benchmark and others, who for months have been privately urging Khosrowshahi to reconsider the autonomous driving strategy. During ATG's short history, it has made progress building and testing autonomous driving systems, but also struggled amid a damaging lawsuit brought by Waymo, a tragic pedestrian fatality caused by one of its autonomous cars and the sector-wide reckoning that even the most basic self-driving vehicles will take significantly more time and money to develop than previously expected.
Announcing the news in a joint statement after the market closed Monday, Aurora and Uber said the group would focus on driverless trucking first and later more complicated light vehicles carrying passengers.
"It works well for both of us," said Aurora CEO Chris Urmson in an interview Monday. "We're excited to have them team with us, and we're excited to have Dara join our board."
Aurora's co-founders have a deep history in the self-driving industry. Urmson previously led Google's self-driving team, which became Waymo. Sterling Anderson directed Tesla Inc.'s autopilot efforts, Chief Technology Officer Drew Bagnell, an associate professor at Carnegie Mellon University, was part of the 2015 academic exodus that formed the Uber's ATG team. Bagnell left ATG to co-found Aurora.
Aurora earlier this summer expanded testing on public roads from California and Pennsylvania to include Texas, with an initial focus on completing long-haul commercial trips instead of the more complicated urban maneuvers where there are more variables and opportunities for failure.
Having raised $765 million from investors including Index Ventures, Sequoia Capital, T. Rowe Price and Hyundai Motor Co., Aurora was valued at more than $3 billion last year, according to research firm PitchBook. Amazon.com Inc., which purchased its own self-driving startup, Zoox, earlier this year, is also an investor.
Aurora has roughly 600 employees, while Uber's ATG group has about 1,200 employees, many of them based in Pittsburgh, long an epicenter of robotics thanks to Carnegie Mellon University.
Khosrowshahi had sold about 14% of ATG to partners SoftBank, Toyota Motor Corp. and Denso Corp. for $1 billion in 2019, but the unit was burning roughly $500 million a year and was set to exhaust funds by the end of next year, people familiar told Bloomberg this fall.
Even after combining forces, Aurora and ATG face stiff competition from more developed and better funded rivals. Waymo, which has logged millions of miles in more than two dozen cities, announced earlier this year it had raised $2.25 billion from auto manufacturers and private equity groups to expand to new locations.
TechCruch earlier reported that Aurora and Uber were discussing a deal.
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Home > Hardware > Lenovo Profits Rise As Microsoft Chooses Yoga 3 Pro Over Surface Pro 3
Lenovo Profits Rise As Microsoft Chooses Yoga 3 Pro Over Surface Pro 3
By David Richards| 6 Nov 2014
Hardware, Industry, Latest News
The Company who is already a major player in the Australian business to business market is expected to report a net profit of $260.3 million for the three months through September, up from $219.7 million a year earlier, according to a poll of analysts surveyed by Thomson Reuters.
Revenues are set to climb to $11.32 billion up from $9.77 billion a year earlier.
Earlier this week Microsoft chose to take on Apple's MacBook Air not with their own Surface Pro 3, instead the giant software Company chose the new Lenovo Yoga 3 Pro which was launched in Australian retail stores JB Hi Fi and Harvey
Norman last week.
Also last week Lenovo completed its $2.91 billion acquisition of Motorola Mobility with the PC giant who is teaching the likes of Hewlett Packard, Dell and Toshiba how to operate in the PC marketplace set to enter the Australian smartphone market next year with both a Motorola and Lenovo smartphone offering.
Combined with Motorola, Lenovo is now the world's third-largest smartphone maker, according to research firms. Lenovo is already one of the largest smartphone makers in China, and the company has been expanding rapidly overseas for the past year, especially in emerging markets such as Southeast Asia and Eastern Europe. Motorola will continue to sell smartphones under its own brand name.
Analysts are closely monitoring developments in Lenovo's own smartphone strategy, and how well it can coexist with Motorola. Motorola will likely expand into more markets around the world under the Lenovo umbrella, and analysts will be watching for product launch plans.
Now seen as the innovator in the PC market using design teams based in the USA the Chinese Company is seen as "breadth of fresh air" by retailers.
Richard Murray the CEO of JB Hi Fi said "Lenovo is a key brand for us, we have great expectations for their products which are right up their".
Cameron Trainer another senior JB HI Fi executive said "The Lenovo brand is stunning we have been working behind the scenes with them for some time and we are very bullish about the growth that the brand can deliver in the PC market".
In an interesting Microsoft ad now available on YouTube the weaknesses and the strengths between the Mac Book Air and the Lenovo Yoga 3 Pro are played off. Quite literally, both the devices dance around each other as Microsoft rejects their own offering in an effort to prove the value of Windows running on a PC platform.
According to the video, Apple MacBook Air comes with a 16 mm thickness, whereas the Lenovo Yoga 3 is only 13 mm thick. It also showcases how Mac cannot perform the Yoga 3 Pro's "tent" move. And how the Apple device does not have a touch-screen yet and also how Mac can never be called a tablet.
The Lenovo Yoga Pro 3 also has a "killer" display claims Microsoft as well as a high-resolution touchscreen display.
David Richards
David Richards has been writing about technology for more than 30 years. A former Fleet Street journalist, he wrote the Award Winning Series on the Federated Ships Painters + Dockers Union for the Bulletin that led to a Royal Commission. He is also a Logie Winner for Outstanding Contribution To TV Journalism with a story called The Werribee Affair. In 1997, he built the largest Australian technology media company and prior to that the third largest PR company that became the foundation company for Ogilvy PR. Today he writes about technology and the impact on both business and consumers.
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Toshiba On The Outer As Six Brands Dominate PC Market
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Have you tried the newly introduced items in their menu? Let me know your thoughts on it.
Call them at the nearest branch around you!


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31 May by Melissa Norris
Keeping a Family Milk Cow- 8 Things You Need to Know
Cattle, Livestock, Raising Your Own Food
Some of the links below are affiliate links, which means I will earn a commission at no additional cost to you, if you click through and make a purchase. Regardless, I only link to products we use on our homestead or believe in.
Keeping a family milk cow or having a home dairy on the homestead is something I've long considered. Grass fed organic raw milk at he store is hard to come by… and you're also paying more for all that wonderfulness.
Dreams of cream, farmers cheese, cream cheese, buttermilk, glass jars of creamy white milk lined up on the counter all from my own barnyard… yeah, this is the stuff a homesteaders dream is made of.
But, we've not yet embarked on this venture. We do raise all of our own meat but milking a family cow and committing to doing it every day has held me back.
Which is why I brought on Jill Winger of The Prairie Homestead to ask her all my burning questions of having a milk cow.
Jill is also one of the presenters in the Modern Homesteading Summit, a completely FREE event starting Sunday June 10th, to catch over 27 homestead presentations click here to learn more
Listen below to, Keeping a Family Milk Cow- 8 Things You Need to Know, Episode #144 of the Pioneering Today Podcast,where we teach families how to grow, preserve and cook their own food using old-fashioned skill sets and wisdom to create a natural self-sufficient home, with, or without, the homestead.
How much milk does a dairy cow produce in a day?
Jill: It really depends partially on the animal, but it depends on your milking schedule, which I think that is a really important aspect to take into consideration when you are dreaming about this home dairy idea.
I call my milking method the "lazy" method. There's this idea that oh my gosh, if you have a dairy animal you can never leave your house, and you're doing chores without fail, twice a day, and it's just brutal.
The more traditional pattern is where you have your dairy animal, they have their baby, you take the baby away, feed it a bottle and then you milk twice a day for the rest of your life.
How to Share Milking – AKA the Lazy Way to Milk a Cow
But, we have to, what I call "share milking". When we share milk, we leave the baby, whether it's a goat or a calf, on the mom for 12 hours.
They go out in the day and they graze and then they play in the sun. And then at night, we will put the baby in a pen with some hay and water bucket.
The udder will fill up overnight, and then we go out first thing in the morning and milk. The baby goes back with the mom for the rest of the day.
If you use the share milking plan, you're only going to be milking one time a day, you'll only have half of the commitment that you would have had prior. I'm telling you all this story in a round of a way to answer your question about how much.
If we're milking once a day … Like, with our cow we get about one and a half to two gallons per milking. One and a half to two gallons in the morning, and if you are doing it again in the evening, it would be another one and a half to two gallons. You're looking at three to four gallons a day, I think, from your average cow.
Melissa: That's a lot of milk.
Jill: It is, yeah. And the share milking helps reduce that, cuts it in half obviously, but still two gallons a day, that's a lot.
When to start milking a cow after calving
Melissa: When they first calve, when that baby is a newborn, do you immediately start this, or do you give them like say two weeks, three weeks, where they're with mom 24/7 nursing before you start doing the share milking? What's that timeline like?
Jill: I leave them together for about two weeks just to give the baby and the mom time to bond. The other thing is you want the colostrum to come in and then kind of flush out. The colostrum, for those of you who aren't familiar, is the first milk, and it's really sticky and thick, and really golden yellow.
It contains all the good stuff that that calf needs, and it's not as yummy for humans to drink. You can drink it, it's just not as good. Most people skip the colostrum. It will be gone in a few days, but I like to make sure they get all the colostrum, they have lots of bonding time, and then about two weeks later I'll start the share milking process.
Does the amount of milk you get per milking change as the calf grows with shared milking?
Melissa: Do you notice the calves when they're three to four weeks ago, and then at two months old, is there a big difference in how much milk you're getting, or does it just pretty consistently stay the same?
Jill: I'm trying to remember if I noticed a huge difference. One thing I will mention, and it probably wouldn't be as prevalent in a beef breed, but like with our very mature milk cow … She's, I think, seven or eight this year, which is hard to believe. But her bag is really big. She's had lots of calves, had lots of calves on her, so she has this big udder.
When she has one little newborn calf who's not drinking as much, sometimes I do have to help her out within those first two weeks of afterbirth. She has such as huge quantity, and the calf can't drink that much, and I just don't want her to get mastitis. I will help milk, I don't usually drink it at that point because it's got a lot of colostrum in it.
As far as supply and demand, I guess I haven't noticed a huge difference because the cow really does adjust to what the calf needs. So, if they're drinking a little bit, they'll produce that amount of milk.
Managing 2 gallons of milk daily
Melissa: If I get one and half to two gallons of milk a day, that's a lot. If you start to get backed up, like you're not able to use it all, then do you just … because the calf is on her, then you'll just kind of skip a day and maybe just leave the calf with her 24 hours until you're ready to milk again? Do you do that? Or, do you find that you really do go through that amount of milk that much every single day?
Jill: I like to leave the calf on. Honestly, I'm being transparent here, slightly embarrassing, I haven't milked our cow very much this spring. We've had a lot of traveling, I've been working on a cookbook, I've got a lot of projects, and I've just been I guess, lazy, or maxed out, I don't know what it is. But yeah, you can totally do that.
That is a benefit because I have had periods where we haven't had a calf on and I have been milking solely, just me, and it's tough.
I mean the fridge fills up quickly, and unless you're selling the milk, which that's not legal everywhere, but unless you're selling the milk, or you have a hog that you can give the access to, it's actually a stress to be like, "What do I do with all this milk? I just don't want to dump it out on the ground."
We can get romanticized versions about anything in life, but especially with homesteading because having your own milk supply, getting to make cheese, that is awesome. But there's a reality side of it. I'm so glad that we're talking about his in real life, the true reality.
What's your average or normal routine, or ways that you work with the milk?
Jill: My pattern is I skim the cream pretty much off of everything.
Side note: since we have talked about share milking so much, often with a lot of cows, not all of them, but they're super smart and they know that you're milking them. They're letting their milk down, you're filling your bucket. But they know their calf is in a pen around the corner so they will actually save back what is called "behind milk".
So, there's "before milk", like before. And then "behind milk", like hind leg. So, before and after. They'll save that hind milk back. So, you'll be milking and the udder will feel empty, then you let that calf in with the cow and all of a sudden that next letdown of milk will come and it will have milk dribbling out of it's mouth. But, behind milk has the most cream. It's the richest.
I noticed that I'm share milking, I don't get as much cream as I would if I was milking twice a day. A little bit of a bummer. I'm still getting several inches on each gallon, but not like those eight inch cream lines when there's no calf.
Home Dairy Milk Handling Procedure
Let the milk sit in the refrigerator for 24 hours, that lets the cream rise to the top.
Skim it off with a ladle and put it in a separate jar.
The milk is left. It's still 1,000 times better than the skim milk at the store, even though it could be called skimmed milk.
Ways to Use Your Excess Milk
Drink it of course.
Use it in recipes.
Yogurt. I will make that milk into yogurt, to make like a gallon of yogurt at a time, or more. How to Make Yogurt without a Yogurt Maker
Homemade mozzarella. That's one of my favorite, just easy, cheeses to make that it will use up two or three gallons at a time. How to Make Mozzarella in 30 minutes
Cheese- learn how to make homemade gouda cheese at home in Corrina's presentation in this year's 2018 Modern Homesteading Summit, click here for details
Ice cream Simple Homemade Vanilla Ice Cream Recipe
Butter, as much butter as possible.
Free livestock feed. When we have leftover beyond that, or I have way left over from making cheese, I will often give it to the chickens, or if we have pigs, I will feed it to them.
Organic fertilizer. Or, if I'm really, really maxed out, I'll even dilute it way down and just put it in the yard as a fertilizer. There're ways to use it, obviously, you just have to be a little creative.
Do you need to pasteurize your milk
Jill: That's kind of why we were interested in the milk cow in the first place, because I had done a lot of reading and research on raw milk. I decided that I liked the idea of the health benefits it had. At that point in time we lived in Wyoming, and it was very illegal to purchase raw milk.
So it was like, well, milk cow or nothing. Yeah, it's a personal decision. You can get a pasteurizer and go that route if you like. We prefer it raw. I do strain it, we keep it cold, and we keep it clean. So I am very careful with how we handle it, but I really love raw milk. I'm a huge fan.
Melissa: I am too, and we live in Washington State. We can purchase raw milk here. Of course, it is more expensive than the non-pasteurized route, but I would be following in your footsteps when we get our dairy cow, and going raw milk.
Mainly, my father grew up and they didn't have a refrigerator, they didn't have electricity, they had a pump in the kitchen, a hand pump, and an outhouse. That was how my grandma did everything, was with raw milk.
How to Keep Milk Cold without a Fridge
They actually had a little creek, a little water area, dug out into the side of a hill because it stayed cool there. It was kind of like a root cellar, but there was … Actually, kind of a slash between a root cellar and a spring house. That's where they would store the milk. It was a large family, and so they were going through their milk a lot. To hear this special interview with my dad who grew up during the Great Depression go to 17 Self-Sufficiency Tips from the 1940's & Great Depression Live Interview
Raw Milk or Not
Melissa: Everybody, of course, has to do their research. With raw milk, there are risks … you've got to be very clean. Of course, everything has its risk. But I'm with you in going the raw milk route as well as it's not as much, so then you don't have to heat everything, and then wait for it to cool and the re-bottle it, and that type of thing, too.
Jill: Yes, I love that … I like to say, and I'm sure there are limitations on this, but I like to say that raw milk really doesn't go bad, it just changes forms. Which, I'm sure it can go bad eventually, but you know, it's a living food. It's the sweet milk, and then it clabber's, and then you have your whey. And the whey always last in the fridge a long time, so it's just cool how you can just … It just keeps giving and giving. There are just so many options you can do when you do keep it raw.
Melissa: Especially when it's from your own cow because I know with our own animals, I know they're not diseased, they're being taken really good care of. I think when you have a really healthy animal that those risks are lowered a lot more than trying to do raw milk from a commercially raised farm. That's when I would have a concern personally.
Jill: Absolutely. I have people email me questions, "Aren't you scared? Aren't you nervous?" There's risk with anything you put in your mouth. The stories we've heard of fast food chains getting people really sick. There's always a risk.
Melissa: I am so glad that you came on here and we had this conversation because I really feel that doing it that way, the way that you've presented to us, is going to be so much easier than being, like you said, married to the cow.
To catch Jill's full presentation in this year's 2018 Modern Homesteading Summit, Everything You Need to Know About a Home Dairy- Pros and Cons of Goats vs. Cows, click here to snag your seat
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Our Food Production Plan & How to Plan for Livestock
5 Tips on Raising Livestock for Food
12 Tips on How to Raise Pigs for Meat
How to Keep Animals Cool in Hot Weather
Maximizing Your Homestead for Profit & Production (With Joel Salatin)
Commonly Believed Homesteading Myths
Filed Under: Cattle, Livestock, Raising Your Own Food
Melissa Norris
Melissa K. Norris inspires people's faith and pioneer roots with her books, podcast, and blog. Melissa lives with her husband and two children in their own little house in the big woods in the foothills of the North Cascade Mountains. When she's not wrangling chickens and cattle, you can find her stuffing Mason jars with homegrown food and playing with flour and sugar in the kitchen.
Read more about Melissa
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Melissa – I have long been a fan – – – I used to have a cow and milked her for years – – – I am just having a problem getting this calf in somewhere – oh my. Any helpful hints as to how to get this baby put away a little easier? The first night I gave up and put mama away – – – my last cow was sooooo easy compared to this one. She is skittish – but MOST of the time will come for food – not always esp. now that we are messing with almost 3 week old baby
Erika Clover
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