Why do certain hybrid combinations change depending on gender?

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Like for Ligers and Tigons. Liger is almost always larger than the female Tiger and male lion parents, but a Tigon with the reverse parentage gets an animal that stays the roughly the same size as the parents but often smaller

Also why is it that sterility seems to be a scattershot? They have evidence of both males and females being sterile but there are also cases where they can produce.

Also while I’m at it, while does sterility seem to be an absolute in some hybrids while being only hampered or even just fine in others?

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Anonymous 0 Comments

Put simply, some genes have only the mum’s or dad’s copy working properly, using a process called imprinting.

If e.g. lions get a particularly large contribution of “pro-growth” signals from their dads compared with tigers, then a male lion/female tiger pair will end up bigger than female lion/male tiger.

These unbalanced effects can result in hybrid animals either not making it to birth, or making it to birth but growing into a sickly animal that has health issues such as sterility. This sterility may not be complete in every animal, as they all might have different health issues that develop.

Often with hybrids, the sex which is heterogametic (has two different sex chromosomes – like in humans it’s the males, XY) is more likely to be sterile or unviable (and basically never make it to term). This is called Haldane’s rule, and one reason for this might be that in the heterogametic sex – let’s take humans for instance – they only have one copy of the genes on the X chromosome. If they inherit versions that don’t work properly in the hybrid’s development and body, the creature will just die or be sickly; in the XX female, they have another X chromosome that might provide a healthy copy.

I think I answered each question! Let me know if you have any more!