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The Y chromosome only codes for 55 genes, while the X chromosome codes for 900 genes [1]. The Y chromosome self-evidently doesn't contain genes necessary for

The Y chromosome only codes for 55 genes, while the X chromosome codes for 900 genes [1]. The Y chromosome self-evidently doesn't contain genes necessary for basic survival, because females don't have it. Males have only one X chromosome. Each cell in a human female has one X chromosome fully active and another one partially active [2], which means their phenotype, as far at it depends on the X chromosome, has lower variance because of partial averaging. [1] https://www.genome.gov/about-genomics/fact-sheets/Y-Chromosome-facts https://www.genome.gov/about-genomics/fact-sheets/Y-Chromoso... [2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4696107/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4696107/

microcolonel 7y ago
Colour vision being the classic example of something preserved or enhanced in females due to coding on the X chromosome. This helps women, for the most part, completely avoid red-green colourblindness. Coincidentally when searching to make sure I wasn't saying this the wrong way around, I was presented with this weird sexist propaganda[0] that only works because of the weird way people tend to think about these facts: you only acknowledge it if you can make it sound like women are better at everything and make no tradeoffs. [0]: https://www.theguardian.com/books/2020/apr/19/the-better-half-on-the-genetic-superiority-of-women-review-bold-study-of-chromosomal-advantage https://www.theguardian.com/books/2020/apr/19/the-better-hal...
- SamReidHughes 7y ago
  Greater male variance in humans has nothing to do with the article, or general discussion about the evolutionary benefits of sexual reproduction, because what's true of some categories of animal, like mammals, is not true of birds and other animals (whose sex chromosomes work differently -- female birds have greater variance, last I checked).
  - microcolonel 7y ago
    > Greater male variance in humans has nothing to do with ... the the evolutionary benefits of sexual reproduction https://arxiv.org/abs/1703.04184 https://arxiv.org/abs/1703.04184
    - SamReidHughes 7y ago
      Okay, but it's not male-specific.
dogma1138 7y ago
This isn’t about sex chromosomes, we have 1000’s of genes that are sex-biased this means that their expression is dependent on sex. The level of bias isn’t even solely dependent on the gene in question but on much more complex mechanisms that are frankly not well understood for example in humans testicles and mammary glands have some of the highest levels of sex biased expression in of all tissues. Other tissues like brain, heart and muscles also have variance but to overall lower levels (higher brain tissue expression variance in males for example has been linked to higher likelihood of schizophrenia and other mental conditions). Overall males it seems that there is a higher variances of sex biased gene expression in various tissues compared to females. This means that it goes beyond we have a backup X chromosome and gene deactivation escape mechanisms. Gene expression variance can explain why males might a higher overall variance in traits.
- nootropicat 7y ago
  The existence of those mechanisms doesn't mean the increased variance from only one X chromosome disappears - for males to have equal variance the increase from just one X would have to be compensated somehow, which is probably impossible given how directly important X is - the needed information is gone.
  - dogma1138 7y ago
    What I’m saying is that genetic variance and gene expression variance aren’t the same thing. In fact in males there is a phenomenon that is called feminization of gene expression where by removing sexual competition causes gene feminization in males causing the population to more favorably express female bias. https://www.nature.com/articles/ncomms4482 https://www.nature.com/articles/ncomms4482 I can’t find the study now but similar results have been reported in humans especially in sperm and testicular tissue that begin experiencing gene expression feminization rather quickly in monogamous relationships.

microcolonel 7y ago

Colour vision being the classic example of something preserved or enhanced in females due to coding on the X chromosome. This helps women, for the most part, completely avoid red-green colourblindness. Coincidentally when searching to make sure I wasn't saying this the wrong way around, I was presented with this weird sexist propaganda[0] that only works because of the weird way people tend to think about these facts: you only acknowledge it if you can make it sound like women are better at everything and make no tradeoffs. [0]: https://www.theguardian.com/books/2020/apr/19/the-better-half-on-the-genetic-superiority-of-women-review-bold-study-of-chromosomal-advantage https://www.theguardian.com/books/2020/apr/19/the-better-hal...

SamReidHughes 7y ago
Greater male variance in humans has nothing to do with the article, or general discussion about the evolutionary benefits of sexual reproduction, because what's true of some categories of animal, like mammals, is not true of birds and other animals (whose sex chromosomes work differently -- female birds have greater variance, last I checked).
- microcolonel 7y ago
  > Greater male variance in humans has nothing to do with ... the the evolutionary benefits of sexual reproduction https://arxiv.org/abs/1703.04184 https://arxiv.org/abs/1703.04184
  - SamReidHughes 7y ago
    Okay, but it's not male-specific.

dogma1138 7y ago

This isn’t about sex chromosomes, we have 1000’s of genes that are sex-biased this means that their expression is dependent on sex. The level of bias isn’t even solely dependent on the gene in question but on much more complex mechanisms that are frankly not well understood for example in humans testicles and mammary glands have some of the highest levels of sex biased expression in of all tissues. Other tissues like brain, heart and muscles also have variance but to overall lower levels (higher brain tissue expression variance in males for example has been linked to higher likelihood of schizophrenia and other mental conditions). Overall males it seems that there is a higher variances of sex biased gene expression in various tissues compared to females. This means that it goes beyond we have a backup X chromosome and gene deactivation escape mechanisms. Gene expression variance can explain why males might a higher overall variance in traits.

nootropicat 7y ago
The existence of those mechanisms doesn't mean the increased variance from only one X chromosome disappears - for males to have equal variance the increase from just one X would have to be compensated somehow, which is probably impossible given how directly important X is - the needed information is gone.
- dogma1138 7y ago
  What I’m saying is that genetic variance and gene expression variance aren’t the same thing. In fact in males there is a phenomenon that is called feminization of gene expression where by removing sexual competition causes gene feminization in males causing the population to more favorably express female bias. https://www.nature.com/articles/ncomms4482 https://www.nature.com/articles/ncomms4482 I can’t find the study now but similar results have been reported in humans especially in sperm and testicular tissue that begin experiencing gene expression feminization rather quickly in monogamous relationships.