Why do cross-species pairings create some offspring that are infertile and some are fertile?

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It makes sense that two similar enough animals would be able to produce offspring, so in that respect, hybridization seems straightforward.

But I don’t understand why some hybrid offspring—like the liger (lion + tiger)—are fertile and some—like the mule (horse + donkey)—are not. It would seem that if the two species are close enough to produce offspring, that those offspring could naturally be able to mate with other hybrids or the original two species. But it probably only seems that way to me because I don’t understand some of the mechanisms at work here. So my questions are…

1. What determines if a hybrid is fertile or not?
2. Are all fertile hybrids compatible with both parent species and other hybrids or are some more restrictive?

In: 10

3 Answers

Anonymous 0 Comments

A mismatch in the number of chromosomes from the parents. For example a horse has 32 chromosome while a donkey has 31. This mismatch isn’t large enough to prevent hybridization in the first place, but it renders the mule’s sex cells faulty, meaning they don’t work and therefore the mule itself is infertile.

Anonymous 0 Comments

A mismatch in the number of chromosomes from the parents. For example a horse has 32 chromosome while a donkey has 31. This mismatch isn’t large enough to prevent hybridization in the first place, but it renders the mule’s sex cells faulty, meaning they don’t work and therefore the mule itself is infertile.

Anonymous 0 Comments

A mismatch in the number of chromosomes from the parents. For example a horse has 32 chromosome while a donkey has 31. This mismatch isn’t large enough to prevent hybridization in the first place, but it renders the mule’s sex cells faulty, meaning they don’t work and therefore the mule itself is infertile.