Submitted by Which-Community-5851 t3_11njmq7 in askscience

So i have a reporting about the chromosome next week and i saw that the Y chromosome is shorter than the X.Is there something behind that?(and pls help me give out any interesting facts about chromosomes that's normally not told when discussing it so that my report will be a bit more interesting(⁠〒⁠﹏⁠〒⁠) ) thank u ia!!(⁠人⁠ ⁠•͈⁠ᴗ⁠•͈⁠)



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Tropenpinguin t1_jboo3zp wrote

Y chromosome in humans are getting shorter. It loses around 10 genes per million years. At this rate it will be gone in four and a half million years. Also sex-determination doesn't only involve the Y chromosome, but around 60 genes working in concert all over the genome.

You only want human facts? I've got some pretty interesting animal facts for the Y chromosome.


xilog t1_jbps2iq wrote

> Also sex-determination doesn't only involve the Y chromosome, but around 60 genes working in concert all over the genome.

But aren't all of those triggered by SRY, which is (usually) located on the Y-chromosome?


Tropenpinguin t1_jbqmuh9 wrote

SRY is like a conductor. It triggers the multiple genes to express testes or suppress ovaries. But those genes also trigger and suppress other genes. And while SRY is the trigger in some mammals, it's not necessary to kick start sex determination.

For example the platypus has five pairs of sex chromosomes. Females are XXXXXXXXXX and males are XXXXXYYYYY. Despite that many Y, on none of them SRY is found. One of those other interacting genes triggers sex determination. What's even more interesting those various involved genes can be found in similar combination throughout all vertebrae, but the trigger differs.

So while SRY is the trigger in some, it's not the only one.


Tropenpinguin t1_jbqpoga wrote

I actually had to look some infos up again and found another fun (?) fact.

In South America there are nine species of vole (genus Akodon) in which a quarter of female are XY, not XX. Their Y chromosome is complete with SRY, yet they still develop ovaries and produce viable eggs. That suggests they must have a entirely new master switch gene that can suppress SRY.


ScienceIsSexy420 t1_jbq7j32 wrote

I seem to recall learning somewhere that the male chromosome has been seen to disappear as you described, and then reevolved again later on in the same species (or perhaps one of its evolutionary offspring species so to speak). Is this true?


Tropenpinguin t1_jbqox1d wrote

I don't know about that. I'm referring to J. M. Graves, a professor of evolutionary genetics. She looked at how the platypus Y was different to the human Y and calculated how much genetic material had been lost since our species diverged. That's how she got that time frame.

But she also told that some (male) scientists aren't fans of this and try to prove how stable the Y chromosome is.


ScienceIsSexy420 t1_jbqpf3u wrote

Hmmm, perhaps what I'm thinking is that multiple different male chromosomes have evolved in different branches of evolution?


Tropenpinguin t1_jbqqgwn wrote

I didn't hear of something like that, but think it's possible.

If you remember or find the info it would be interesting to know.


legitusernameiswear t1_jbs21nk wrote

Humans diverged from Macaques 25 million years ago and have lost one (1) gene on the y chromosome since then. The Y chromosome isn't going anywhere.


ggchappell t1_jbpav1a wrote

> I've got some pretty interesting animal facts for the Y chromosome.

Let's hear them!


idrather_be_dead t1_jbohyqu wrote

Y chromosome is smaller because it doesn't really contain as much genetic information as the X chromosome does.

X chromosome container several vital genetic information but Y has mostly genetic codes that are often redundant or obsolete and overridden by X except sexual development.

There are some animals like whiptail lizard which only have females because as they evolved their male allosome (the human equivalent of Y chromosome) became redundant and unnecessary.


Octavus t1_jbp1pre wrote

The Y chromosome is unable to perform recombination so most damage is unable to be repaired. This causes loss of genetic information overtime, if the genes were critical to life the animal would be unable to reproduce. So only genetic losses that are no/low negatively impactful can be passed on.


scawneverdies t1_jbprrwn wrote

The Y chromosome is so much shorter than the X because there are much fewer genes & much less genetic information stored in that chromosome. This is because the Y chromosome can’t have any absolutely essential genes, because roughly half the population doesn’t have a Y chromosome and still needs to fully function & survive. The Y chromosome mostly contains genes related to triggering male development, but the genes that actually control male development are on many different chromosomes (including the X).

Everyone has at least one X chromosome, and in fact the X chromosome does contain some essential genes, which also speaks to its length.


babar90 t1_jbol7y7 wrote

See and

Most genes involved in male sexual characters are on other chromosomes but require a cascade initiated by expression of SRY (thus presence of Y chromosome) to be (un)expressed


smapdiagesix t1_jbqje00 wrote

Sometimes SRY gets copied onto the end of an x chromosome during meiosis. People who inherit this end up as xx males.


Joseluki t1_jbpxq94 wrote

It does have just genes for sex determination, so it does not need to be big because it carry not as much information as any of the other chromosomes.

You do not need two X chromosomes active, in fact, in women one of the X chromosomes is inactive and condensed in a Barr body.