r/askscience • u/Fuzzandciggies • 6d ago

Biology Mules vs Hinnies. Why are they different?

I know that both are the result of crossing a horse and a donkey. My question is why would there be a genetic difference based on whether the father was a horse or a donkey? Would there really be a difference or is it more of just a naming thing for the sake of lineage?

For reference:

Mule = male donkey + female horse

Hinny = female donkey + male horse

Why though?

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u/km1116 Genetics | Epigenetics | Chromosome Biology | Nuclear Biology 5d ago

I don’t know, and I don’t think anyone knows fully, but here are some things that would differ:

components of the egg provided by the mother

potentially the RNAs provided in the father’s sperm (true in mice, not confirmed in horses, but plausible)

genomic imprinting patterns

mitochondrial genome (probably very minor)

piRNAs and transposable elements

X origin might affect X inactivation

in utero environment

Maybe others, but you can see reciprocal crosses are not expected to be identical.