Y chromosome

[Watchfulwaiter]

To avoid current derail of thread about Dr Em

This is the most bizarre thread ever. It seems to be a pretty blatant attempt to construct a biological justification to say that women are genetically superior to men. Nasty stuff.

Pair it with the anti-natalism thread (you know, the one where sakura spends a long time making sure we view anti-natalists' beliefs as bitter, misanthropic, daft and evil... but is very keen to emphasise that they're very definitely feminists, then jumps to 'it's the logical next step of radical feminism' and 'they definitely have a point') and one might wonder whether these are sincerely held positions or a ploy to paint those on FWR as crazy misandrist extremists. It certainly makes a change from people plopping in with bile about transgender people and immediately screenshotting it.

Does anyone know what Sakura is on about
Absolutely not a clue lol

books.google.com/books/about/The_Blank_Slate.html?id=G3_UAeo8Dh0C

Slightly more user friendly

Hi, I’m a biologist who happens to study the links between sex dimorphism and sex chromosomes. Here are some tidbits that I hope will clarify:

1. Birds are highly sex dimorphic (much more than humans), yet it is females who have the “degraded” chromosome. Other species have single gene or environmental sex determination and are still sex dimorphic. Male aggression / male specific traits are totally unrelated to the degree of degradation of the sex chromosomes.

2. in XY species where it’s been studied, the vast majority of genes that cause sex differences are on the autosomal (not X or Y) chromosomes. The Y in mammals is basically a trigger and has some sperm genes on it. The X chromosome is “dosage compensated” in most XY species so that everyone gets about the same expression of most genes.

3. Jenny graves is correct but the word degraded is really a technical term. The Y does not recombine for most of its length (except the PAR which is needed to properly segregate the chromosomes during meiosis in males). As a result it is difficult to get rid of mutations. Most mutations are mildly harmful or do nothing. So while the mutation rate on the Y is the same as other Chromosomes, mutations accumulate (build up) on the Y faster. However dosage compensation prevents this from effecting males. As genes degrade, they generally become equalized in expression. Mutations in SRY will NOT be tolerated given the mammalian sex determination requires SRY to make a male so it’s highly unlikely humans will lose their Y completely (though that spiny rat example is super interesting and to my knowledge novel among placental mammals).

4. humans are much less sexually dimorphic than other great apes such as chimps, gorillas and orangutans. We also have biparental care. The trajectory of our species currently appears to be towards reduced aggression / higher pro social behavior. If there’s a heritable basis to higher aggression in human males, it’s being reduced over time. And it’s likely whatever is there is exaggerated beyond recognition by culture (which, by the way, also evolves and has coevolved with humans for millennia).

5. males “evolve” just as much as females. It’s useful to think about evolution at the gene level. A gene on an autosome spends half its time in males, so if possible it will “want” to make the male its in as good as possible. The gene also wants to make good females. If sexual dimorphism exists there may be trade offs for some genes (this is called genetic sexual conflict). The X chromosome is interesting because it’s found in females more often so on balance it may be more likely to carry genes that “help” females since they’ll have more opportunities to do their thing.

I meant to come back on that spiny rat before we went down the rabbit hole of innate evil.

My understanding is that their sex is determined by the expression of zinc finger proteins but I don’t understand how these are activated without the SRY. All I know about zinc finger proteins I learnt from a book on CRISPR where they are used in earlier forms of gene editing.

Also, since the female spiny rat, like the male, has only one X, how does recombination occur? I thought meiosis requires equal numbers of chromosomes since they have to be paired off, eg 23 pairs of chromosomes in humans, including the sex chromosomes.

Thanks FWRLucker - very interesting. Good fortune with your career. My knowledge of genetics only extends to the bacterial and viral kind some 40 years ago, studying TnA Transposons.....wonder if there are such things as 'cisposons'...stay at home genes maybe ?

Oops single point mutation....meant to have been FWRLurker

DH's undergrad degree was in genetics. he came home this evening to a bunch of questions from me that left him with a face like this

thanks to all the scientists posting, it;s very interesting

Oops single point mutation....meant to have been FWRLurker 

This tickled me!

Oops single point mutation....meant to have been FWRLurker smile

A second mutation on the L locus could have made it far worse.

Actually, "women do it too" is a pretty reasonable argument that something is not specifically a men's issue. And that works the other way round as well.

I'm never sure why it gets so much flak. By all means argue that it's factually not the case, or show some important difference. But some things are not sex based issues.

Always
So if females and males are both XO then the X does not recombine. Half of their gametes will get the X and half will get nothing.

What is weird about this is that 1/4 of offspring should actually end up XX, since they would be the product of the fusion of an X egg with an X sperm. Meanwhile 1/4 of embryos would be inviable since they lack an X.

If XX females are NOT observed this implies that XX is inviable. Or there’s some mechanism preventing XX zygotes from forming (like, maybe X bearing sperm and non-X bearing eggs fail to mature). I hope more research gets done on it!

Anyway it’s an interesting example. Mammals and birds are fairly exceptional in that their sex determination systems are much more stable than other groups like fish and insects. In these groups every possible mode of sex determination can be found (single gene, environmental, XY, XO, ZW etc) even differing among closely related species.

I haven’t looked into spiny rat gametes before. I might google so I am going to make a wild guess and see if I’m right. Half of the gametes have an X, the others are unviable. Still don’t know what determines the sex though.

Wait, is there a difference between X0 karyotype and 0X karyotype? In spiny rats, I mean? Does one contain a single X chromosome from the other and the other contain a single X chromosome from the father?

One from the mother, I mean.