Was lobe-like or ray-like more ancestral, or neither?

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For the mules and hinnies that are fertile did they end up with even number of chromosomes or are they fertile despite having odd number of chromosomes?

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Also if you aren't careful she might just kick the stud in the head and kill him. There are a lot of risks for a statistically improbable event where you could just have a gelded male that is useful for work and easier to control, which is why someone would own a mule besides wanting a violent and obstinate pet.

Generally, individuals with an odd number of chromosomes are not fertile. Such individuals cannot make proper pairs of homologous chromosomes during meiosis. Thus such organisms cannot make viable gametes, and hence they are infertile.
But in the real world, nothing is static. There are undoubtedly some exceptions, so there are several species of animals that have odd numbers of chromosomes and are fertile, such as certain types of fish, amphibians, and reptiles. For example, the Mexican tetra fish and the Chinese soft-shelled turtle.

Well, assume mules and hinnies are functionally infertile. Breeding is zero reward, but not zero risk. As well as the risk of injury, there is the risk that a male mule mating with a fertile female will result in a miscarriage of an unviable foetus rather than the young you actually want. There is also a smaller risk than a female mule mating with a fertile male will cause him to be unable to successfully stud for the fertile female you want to breed him with, although this is a lesser concern.

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.

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Not sure about odd or even numbers but potatoes technically reproduce via triploid seeds, triplets instead of pairs of chromosomes. It is why you almost never see actual potato seeds for sale because it is the work of a lifetime to actually breed stable genetics in something like that. I think there may be one or two named seed varieties, usually they are grown from "seed potatoes" which are just potatoes or root tubers, that can sprout. They aren't actual seeds. When they sprout the leaves produce enough energy to produce more potatoes thus repeating the cycle.

Do you want to see something interesting? Check out the Indian Muntjac:

The X fragment is always fused to the autosome, while the Y chromosome stays unfused. So 2n is 6 in females and 7 in males.

Their close relative the Chinese muntjac has 2n=46

And they can interbreed with sterile offspring.

Like an n=3 gamete can fuse with an n=23 gametes and it ‚works‘

They both come from n=70 ancestral deer.

The Indian one just went let’s fuse all the chromosomes.

https://www.jstage.jst.go.jp/article/cytologia/70/1/70_1_71/_pdf

This is true, but it is too simplified.

You can easily have differing 2n in even mammals. All it requires is fusion of only the X fragment but not the Y chromosome.

See the Indian muntjac: https://www.jstage.jst.go.jp/article/cytologia/70/1/70_1_71/_pdf 2n=6/7

Which funnily enough can actually breed with the Chinese 2n=46

Additionally plenty of chromosomes do weird fusion and duplication stuff, meaning you can actually have specific chromosomes that can be dropped with no I’ll effect.

There‘s also insects with males having a single chromosome less than the females.

But that should only possible with ZW/ZZ insects, and not our XX/XY relatives.

And it’s always the case for insects completely lacking Y chromosomes. Take for example stick insects. The females have XX chromosomes the males just have X0 chromosomes.

Like they lack the second sex chromosome in regular existence.

But really as I said: if you have chromosomes that can be dropped wirh no Ill effect, uneven is possible.

And since males are the genetically inferior variant of the ancestral asexual progenitors, usually it‘s the males that will have uneven chromosomes, because their Y chromosome can in many cases do whatever and still leave a fully viable animal.

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.

https://www.jstage.jst.go.jp/article/cytologia/70/1/70_1_71/_pdf

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.

I just wanted to say thank you for this read!

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Lol, I need to read more to make sure I understand, but I will get back to you later!

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