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Thread: A selfish chromosome?

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    A selfish chromosome?

    I have written down some ideas on the y-chromosome. This is the English google translation of a text originally written in German.

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    In 1976, a groundbreaking book for the history of science of the 20th Century, "The Selfish Gene" by Richard Dawkins, was published. Although Dawkins was never one of the leading researchers in his field - from 1995 to 2008 he was a professor of an institute that wants to make scientific findings understandable to a wide audience - the magazine "Der Spiegel" describes him as the most influential biologist of his time.
    Dawkins' special achievement was to reinterpret Neo-Darwinism and Sociobiological insights, opening up an expanded view of the history of life. A central problem of the theory of evolution had been to explain altruism. If the self-assertive will of the individual is the driving force of evolution, as Charles Darwin supposed, we would have to live in a completely selfish world. Why is it possible to observe the opposite everywhere in nature, namely the tendency to forego one's own advantages for the benefit of others? An answer to this question was provided in 1975 by Edward O. Wilson in his book "Sociobiology". Wilson was an ant scientist and found the solution to the problem as he watched the "female soldiers" of social insect states sacrificing their lives uncompromisingly to defend the existence of their polity. Why did they do that?
    Since the individual members of the insect state are infertile and can not have offspring, Wilson concluded that their individual life could not be the highest good, but their genome, which alone can be passed on by the queen to the next generation. The state must live so that the queen can live and pass on the common genes: that is the ultimate state of the ant-state, which completely submits to every individual. It turned out that these principles, which were recognized by the example of social insects in particularly simple, clear conditions, could be applied to all social living animals. In social mammals too, especially for Homo sapiens, the same relationship was found: the more common genes two humans carry, the higher is the mutual willingness to help, to renounce, distinctively. Numerous studies have since confirmed biological altruism.
    Dawkins further developed Wilson's ideas philosophically, presenting them so vividly in his book published only a year later that they were understood by a wide audience. It is not the individual who passes on his genes that is the measure of things - but the genes themselves create individuals as short-lived "vehicles" to move from one generation to the next. We are therefore, as individuals, first and foremost representatives of potentially immortal genes, part of an overall context, of a line of ancestors whose preliminary end point we form; at the same time the starting point of all those generations who come after us. The driving force behind this development, metaphorically speaking, is the will to assert oneself of the genes whose purpose it is to be under the natural conditions and to live on. Dawkins's approach implies a quasi-religious element, defining answers to meaning and being new in a scientific context. That is the reason why in recent times he has become known above all as a critic of religion, the mouthpiece of a scientific attitude that advocates the overcoming of a naive, archaic God-faith.

    The autosomal genes and the Y chromosome

    We have treated the function and meaning of the Y chromosome in detail in our series on haplogroups, so we only want to do so at this point to the extent that is relevant for the present consideration. The human genome, like that of most higher animals, is coded on two equivalent sets of 46 chromosomes, with one half being inherited from the father and the other from the mother. The first 22 pairs of chromosomes are numbered (1-22, A and B ). The last two, X and Y, play a special role. While the other pairs correspond and express individual body characteristics together, there are two possible variations: XX or XY. Anyone who carries two X chromosomes is a woman, the man carries X and Y. The woman passes on one of her two X's to the offspring, the man either his X or his Y. In the first case he has a daughter, in the second a son. This means that the Y chromosome always comes from the father and can be traced back in the direct male line to the distant past. So while the remaining genes branch out and dilute in each generation - only half are passed on - the Y chromosome in the male line is the only true constant and "travels" virtually unchanged from generation to generation.

    It is easy to see that Dawkins's revolutionary vision of genes that travel through the generations fits best directly on the Y chromosome. In the other, "autosomal" chromosomes half of the direct descendants is lost, the next has only a quarter, the next one-eighth - after 10 generations remains, statistically, a genetic match with a certain ancestor of only 0.05 %. One can of course argue that an individual who has children, usually has several offspring and thus not always half, but a smaller part is lost. However, a mechanism whose basic principle is the self-assertion of genes does not go well with the fact that in two-sex reproduction, genes disappear randomly in each generation. One could of course say - and Dawkins would certainly do that - the principle does not require continuity at the level of the individual, the starting point plays no role from the point of view of individual genes. Although they would be torn out of their original context in the body of an evolutionarily successful individual and more and more isolated, but by the correspondingly large number of other descendants of the caregiver, their mere figure does not diminish. But this view is only conditionally agree, because it is precisely the interaction of certain genes that make up the success of the individual. In each generation, the physical and mental properties are redefined by the interaction of the maternal and paternal chromosome sets, each two coincidental genes together form a new property. Darwin's basic idea that successful individuals have more offspring and that their genes continue to spread accordingly loses much of their power of persuasion this way. Without the continuity of certain properties, properties would be re-diced in each generation, and therefore other individuals with other genes would always be successful. Causally more convincing is an idea that starts from successful traits that, precisely because they are successful, are passed on directly from generation to generation.
    Now what do we know about this Y chromosome that travels the generations in the male line? In the imagination of most biologists it plays a meager role. It is considered "crippled," "regressed," having "lost much of its previous characteristics because its central role is confined to determining sex. In fact, it is smaller than most conspecifics and contains about 1.8% of the total genome (with 46 chromosomes, the average proportion is 2.17%). It is important primarily for the expression of male characteristics, such as the sexual organs or the hormone dosage, on the fertility it should have an influence. Recently, it has also been linked to susceptibility to certain diseases. That's it. The Y chromosome is the only constant in the lineage of higher animals. Should nature, whose ordering, evolutionary principle aims to produce something lasting in an otherwise chaotic environment, have produced it in vain? Should it possess this key to the continuous development of life without using it? In any case, it should not be involved in the manifestation of somatic, ie physical and mental characteristics. The genes for this are, according to widespread conviction, exclusively on the autosomal chromosomes (1-22, A / B ). Thus, those 1.8% of the genome lying on Y would be mostly garbage without function. More likely, however, is that they have not been understood in their function so far. In this context, it is interesting to note that even the genes for explicitly male characteristics are not coded for Y but for the autosomal chromosomes 1-22. At the beginning of the pregnancy, so far as we know, a sequence on Y becomes active (SRY: Sex Determining Region on Y), which "activates" certain autosomal genes and thus initiates the development of the testes. Should this be a singular event - an evolutionarily developed function that occurs only once?
    It is quite conceivable that we have discovered the basic principle of how Y works: triggering genes release certain other protein-forming genes in the autosomal chromosomes and initiate physical development. Then Y would be the control center of the emerging body, accessing the huge "dataset" of the existing genome. The genome would be a giant disposition archive, a potential from which Y can select genes and turn them on according to bias. That would also explain why a large part of our genome is classified by researchers as unused genetic waste. Or, to use Dawkins’ metaphorical, anthropomorphic language, the egoistic Y-chromosome would be the driving force, the constant of evolution, and, in creating the body, would draw on the vast dispositional mass of those genes that are currently available to it. This explains why many people who have had a genetic test feel intuitively related to the members of the same haplogroup.
    While the other chromosomes systematically exchange (recombine) genes with their analogous partners, X and Y can not do so because they are fundamentally different in their structure. Only on a small section does a recombination take place. It would be conceivable that Y would give information to the X who will receive his daughter. In this way important traits linked to the continuity of the male line could also be transferred to the female offspring. Also, the fact that women as a partner usually prefer men who are similar to their fathers becomes understandable. If these assumptions prove correct, this would have far-reaching consequences for the self-image of man. Not only the relationship of the sexes would be in a new light, also the events of the world history would have to be reinterpreted under the given conditions as opposition or cooperation of the carriers of different haplogroups. However, this should be done in the context of another essay.

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     JLJD (09-07-2019)

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    Scientists are now shedding new light on the Y chromosome, and have suggested that itís more important than we have appreciated. [...]

    Although the contributions of genes on the male sex chrY have long believed to be restricted to their effects on reproductive functions in sex organs, increasing evidence indicates that their impact may in fact extend to somatic cells as well. [...]

    https://www.labroots.com/trending/ge...38fVIMxokf9n6g

    https://www.nature.com/articles/s415...F-VAtuO_wLT_l0

  4. The Following User Says Thank You to Kaltmeister For This Useful Post:

     JMcB (09-27-2020)

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