The Y chromosome is not vanishing | Hacker News Reader

The Y chromosome is not vanishing

nature.com

21 pointspwrfid19 comments

She says that two species of spiny rats in Japan have lost the mammalian Y chromosome completely, shifting many genes to other chromosomes.

That's interesting! Let's ask the google:

Although they have no Y chromosome, this species still has males and females. In the opinion of Asato Kuroiwa, an associate professor at Hokkaido University, "A new gene formed within an autosome, replaced SRY and became the switch that determines gender." [0]

[0] http://ajw.asahi.com/article/behind_news/social_affairs/AJ20...

Curiously, they don't say how the switch in the rats flip-flops. The article notes that crocodile sex is determined by the temperature of the egg, which is also fascinating -- but how would it work in mammals?

My reading of that statement would be that the presence of the hypothesized "new gene" would produce a male while its absence would produce a female. After all, that's how SRY works, which it is hypothesized to replace. Presumably this new gene would code for a very similar set of proteins to that coded by SRY.

ISTM that there must have been some period during which both the new gene and SRY were present in the breeding population, and the inheritance of either (or both) would have produced a male. Since we're talking about fairly small populations on these islands, it was just luck that caused SRY to disappear before the new gene. I doubt we'll see this occur in larger, more-geographically-distributed populations.

But wouldn't that just make whatever chromosome carries this gene the new allosome? I was reading the statement as SRY moves to an autosome and then some other process regulates expression.

FWIW, biology was the one science course I never took, so I have no idea what I'm talking about.

But wouldn't that just make whatever chromosome carries this gene the new allosome?

Haha, maybe so, I guess that's a matter of definitions...

I was reading the statement as SRY moves to an autosome and then some other process regulates expression.

SRY translocation is not unheard-of (cf. SRY-positive 46,XX testicular "disorder"), but that's not what Prof. Kuroiwa is saying. He's talking about a change that allows a different gene to code the same proteins that SRY codes. That change could be to the gene in question, or to something else that governs how it is expressed. There's a whole family of genes (SOX) that exist all over, on both allosomes and autosomes, which are similar to SRY, and one would imagine these might substitute for it. Looking around a bit more, I find wikipedia links to a paper [0] that claims the substitute SRY is actually a group of multiple genes on X, which group of genes did translocate from Y. Fascinating stuff!

[0] http://www.ncbi.nlm.nih.gov/pubmed/12900579

If the Y chromosomes contains vital genes, then how do women, who don't have a y chromosome, survive?

They have two X chromosomes.

The Y chromosome contains vital genes, for males, that code for things males need. Its really pretty much that. Take away the Y chromosome and most mammal species aren't going to survive. Even the rats that lost it had the equivalent genes on the X chromosome. The gene expression of females isn't the same as males in short. In spite of the fact that females and males share an X chromosome.

The Y chromosome doesn't contain vital genes, in fact by chromosome standards it doesn't contain many genes at all. The primary role of the Y chromosome is as an activator and modifier of gene programs that reside all over the genome. This makes sense because the male anatomy is mostly just a modification on top of female anatomy (preventing some growth here, promoting some other growth there... done).

That said, I don't think it's possible to create a fully fertile male by forgoing the chromosome and just giving hormones - there might be some very few sex-specific proteins on it, but I think it depends on the species.

That's what I thought but then the article says this:

"""

The Y has been stable for the past 25 million years, scientists say. And a major reason is that many of its remaining genes are crucial to the survival of all humans, going far beyond sex determination. There are genes that affect protein synthesis, how active a gene is, and others that splice RNA segments together. They are found in the heart, the blood, the lungs, and other tissues throughout the body. “These are powerful players in the central command room of cells,” says David Page

"""

I guess it depends a bit on what genetic regions we're talking about but to my knowledge since the Y contains so few genes it's not surprising that almost none of them changed for a long time. It's already very stripped-down. I'm far less sure about non-coding regions though, I'd have to check up on that.

From what I can tell the text doesn't contain a lot of new or surprising information, but it does present it in a misleading way.

It's clear that sexual dimorphism in humans is profound in some respects and superficial in others. Since the Y chromosome regulates sexual development, and since males do get some metabolic modifications, saying the Y influences protein synthesis in vital tissues is mostly a truism.

Saying that for example autoimmune diseases with lopsided sex distributions are not connected to sex determination is a fruitless semantics game disconnected from the actual science. To be fair, it's not any more sensationalist than the "rotting Y chromosome" spiel which has been in the press earlier, but all of this is really more a testament to all the things that are wrong with science reporting (and the scientists who enable it) than anything else.

Well that's the question - if it's "crucial to the survival", then how do ~50% of all humans survive without it?

The article does makes a point that unimportant genes have been eliminated from the Y. However, if the remaining genes and relevant proteins are beneficial (as opposed to mandatory), then it would still make sense in the [very] long run that those genes would migrate to some other chromosome, be beneficial also for female homo sapiens, and then get eliminated out of the Y as redundant there (since they'd be somewhere else for both genders already)

Some (maybe most) of the genes in the Y are only useful for men. Others of the genes in the Y chromosome are “vital”, but the X chromosome has a copy of them. So the men have two copies of these parts.

In women, one of the X chromosomes is inactivated, so it’s almost like that each cell has only one (active) X chromosome. The shared part is not inactivated. So both men and women have two active copies of these parts, and only one active copy of the not shared parts.

Read: http://en.wikipedia.org/wiki/X-inactivation

More specifically: http://en.wikipedia.org/wiki/X-inactivation#Expressed_genes_...

Which is more detrimental to the survival of a certain gene, losing vital data or gaining useless data.

Some genome sizes, the marbled lungfish carries a lot of weight in its cellular nuclei.

ftp://www.fourmilab.ch/pub/goldberg/sizes.html

Awww, it's okay boy, you'll survive even if gender is not fixed the way you thought it were and even if your gender becomes irrelevant.

It's not gender identity, but biological sex that's the issue here, which is kinda important when it comes to reproduction.

Well, we are close to capability to ignore biological sex when it comes to reproduction. We probably don't/won't want to ignore it, but if we had to, then we most likely could make do with artificial means of reproduction that don't neccessarily need both sexes.

But we're not there, and even if we were, the methods are vastly more expensive and inaccessible than natural methods.

Sure, if we could then biological sex wouldn't matter quite so much, but until we are, the old Y chromosome is still rather important.

If we're talking about a chromosome going away quickly, then "quickly" in that context means at least thousands of generations. We're not there, but it's not that far away.

Oh, I agree, and research down that line is worth pursuing, but until we're at that point and Y is still important. The implications would be staggering, and no doubt mostly for the better. It could open up the ability to have children to so many couples who currently have few options, be they same sex, infertile, or whatever. The primary downside I can see in the short term is the effect it would likely have on adoptions.

That said, part of me would prefer is we didn't need to rely on non-built-in means to propagate. The idea of becoming utterly reliable on a particular piece of technology for our survival as a species isn't one I'm fond of.

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