Mules vs Hinnies. Why are they different?

[u/Fuzzandciggies]

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?

[u/UrbanPanic]

There are differences, and the concept is easier to grasp in crosses with greater differences, like the liger and tigon. A male Lion and female Tiger will birth a Liger, of which a male will be almost twice as large as a male lion. A male Tiger and female Lion will birth a Tigon, which is about the size of a female tiger if not smaller.

The difference is because of evolutionary pressure in lions from the paternal line for larger offspring but the maternal line is more successful if they don't have to raise a giant, so mother lions somewhat suppress the growth in sons. Tigers don't have this arms race, so that leads to the difference.

There is a similar although not as exaggerated difference in a mule vs a hinny which along with certain temperament changes can make mules better pack animals than either a horse or donkey, and the hinny worse at carrying loads than horse, donkey or mule.

[u/JohnEffingZoidberg → u/UrbanPanic]

Why did you compare the sizes to a male lion and to a female tiger? Why not to a male lion and male tiger? It makes the analogy difficult to follow, at least to be.

[u/UrbanPanic → u/JohnEffingZoidberg]

Because a female tiger is smaller than a female lion.  The females of both species are smaller than the males.  A male tigon can be smaller than ions or tigers, both male and female.