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Biologists Debunk the "Rotting Y Chromosome" Theory

Posted by samzenpus on from the men-of-the-future dept.

An anonymous reader writes "Biologists have previously predicted that that the male sex-determining Y chromosome, which once carried around 800 genes, like the X, has lost hundreds of them over the past 300 million years, will mutate itself out of existence, leading to the eventual extinction of men. However, researchers of a study published in the latest issue of Nature found evidence to suggest that the Y chromosome will not shed any more of the 19 ancestral genes that it is left with."

5 of 248 comments (clear)

  1. Both sexes are valuable by Anonymous Coward · · Score: 5, Interesting

    While our Y chromosome may make us (men) more susceptible to genetic diseases, it also allows for more rapid adaptation and spread if a mutation is beneficial. I certainly wouldn't want it to go away.

    1. Re:Both sexes are valuable by Darinbob · · Score: 5, Interesting

      Except that they were talking about the Y chromosome. The problem with it is that it doesn't get combined with genetic material from the mother, it's passed on as-is. So over time it can degrade due to mutations, and it has done this in the past. However natural selection is strong enough to maintain it.

    2. Re:Both sexes are valuable by reverseengineer · · Score: 5, Interesting

      Well, there's no specific reason to favor the XY system of sex determination over some alternative arrangement, like the ZW system in birds (females are ZW, males are ZZ). In that case, the Z chromosome is larger and has more genes than the W. On the other hand, there's really no evidence to suggest that the XY system is any worse than the alternatives, or at least worse enough to support some sort of changeover (or lead to the extinction of placental and marsupial mammals). It does make sense to let Y "rot" to a certain extent: letting Y "cross over" with X is hazardous. It leads to the possibility of producing gametes that contain X chromosomes with male-sex determining genes, and gametes that contain Y chromosomes that lack those male-determining genes. It is to the system's benefit that X and Y are completely non-homologous, even factoring in the problem of X-linked diseases. It's theoretically possible that the function of Y could be captured in a single gene. However, chromosomes are also physical structures that have to be able to be manipulated by the machinery of the cell. It's likely that there is a minimum size for that to be done without high risk of error, which means that Y is safe.... for now.

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  2. Why would anybody think otherwise? by Rich0 · · Score: 5, Interesting

    So, genders have been around for hundreds of millions of years - why would anybody think that evolution would suddenly make them go away?

    In humans it probably doesn't make so much sense to have lots of sex-linked characteristics, so it makes perfect sense that the contents of the Y chromosome would dwindle over time to just the minimal set of genes necessary to confer gender. After that there should be strong selective pressure to conserve things.

    Suppose for the sake of argument somebody is born with a Y' chromosome that doesn't confer maleness. Either they'll have non-functional reproductive organs, or functional female ones. In the former case they're an evolutionary dead-end. In the latter case and they reproduce with an XY man then 25% of their children will be normal XX females, 25% will be Y'Y offspring that won't make it to birth lacking an X chromosome, 25% will be normal XY males, and 25% will be XY' like the mother. So, in 75% of those cases the Y' chromosome is lost. And all that assumes that there aren't any deformities/etc that make reproduction less likely. I can't see how such a situation could ever become dominant. It would likely reach some low frequency equilibrium even if not harmful.

    The fact that it hasn't already happened makes me think that it is not likely to do so.

  3. Re:correct me if I'm wrong by Michael+Woodhams · · Score: 5, Interesting

    They Y chromosome not only evolves fast because of lack of recombination, but also because sperm are very many more cell division generations away from the original copy (fertilized ovum) than ova are. The Y chromosome spends 100% of its time in males, normal chromosomes 50%, X chromosomes 33.3%.

    Ref: "Male-Driven Sequence Evolution", pg 225, "Molecular Evolution" by Wen-Hsiung Li (1997).

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