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TheBloxyBloxGuy OP t1_jbhl65t wrote

What's really interesting is that I have found multiple examples of organisms with odd-numbered males and even-numbered females, but I can't seem to find a single odd-numbered female.


EmilyU1F984 t1_jbie16i wrote

It‘s the Y chromosome in Indian muntjacs that‘s added on.

Or rather the Y chromosome doubled at some point, with one of them becoming a non sex determining variant.

Since a ‚functioning‘ Y chromosome that determines sex only actually needs a single gene to switch from the normal female type to the male type; it can get pretty wonky without much trouble.

I‘d assume in other species it‘s the same.

Also the X chromosomes in Indian muntjacs is stuck into a different chromosome.

So the female muntjac has two ‚regular‘ chromosome pair, one pair with a tiny X portion stuck to the two tops. While the male muntjac has the same two regular pairs; and then the next pair has the X portion only stuck to a single one in the pair, and the Y being a tiny additional chromosome.

So really, the males have a higher number of chromosomes because their Y chromosome is free floating and doesn‘t ‚attach‘ to the spot where the second X would go in females

As single X chromosome individuals are perfectly viable in virtually all species, it seems the Y chromosome can really do whatever it wants and things will still work.

Btw the Chinese muntjac has 46 chromosomes and can interbreed with the Indian muntjac with 6/7 chromosomes.

And the change from the 46 variant to the 6/7 one is pretty recent.

Like they have the same number of genes. They just Stuck all those 46 chromosomes together in a very chaotic way for some reason.

While staying perfectly healthy throughout.

For the chromosomes.

Since the Y chromosome is the ‚inferior‘ variant of the X chromosome, I.e. it carries virtually zero essential genetic information, because only XX individuals are ‚whole‘; it is much more free to just ‚be‘ and still work.

It really only needs the SRY gene and it‘ll work.


Dr_Vesuvius t1_jbihbun wrote

From this logic it would follow that in species which don’t use the Y chromosome to determine sex, like birds or crocodilians, we would expect to see different patterns.


viridiformica t1_jbkeika wrote

Seems like it's still contentious, but since avian sex regulation appears likely to be dependent on having two copies of the Z chromosome to induce maleness, the W chromosome that females have is likely to be analogously expendable to the Y chromosomes - so you would see the same patterns just with the sexes flipped?


Navvana t1_jbism7z wrote

Do a general search for sex-determination systems. There are all sorts of patterns that can arise from other systems that aren’t XY.

In particular ZO/ZZ sex determination where the female only has one sex chromosome and the male has two.

It only occurs in some species of moth though.


lostmyselfinyourlies t1_jbj4gqk wrote

Not relevant to the original topic but it blew my mind when I found out that there are mushrooms with thousands of sexes. Super weird little fungi :)


Navvana t1_jbj7blc wrote

Yea Fungi mating types aren’t so much sexes as we understand them and more decoder rings.

It’d be like if we had 4 sex chromosomes instead of two, and multiple letters instead of binary.

XAYZ sex vs LBXK sex, and you can only mate with someone whose every chromosome is different.

That, in very broad strokes, is the method behind some fungi reproduction. Others are pretty analogous to human sexes. It’s a very wide range of strategies with fungi.


WendysForDinner t1_jbjj4ug wrote

I see why mycologists claim there are thousands of unidentified species of fungi. It makes sense that many variants would occur.