Problem:

I've read a little about hybrid animals, and have been amazed by the fact that the gender of the parent species determines the species of the offspring, in some hybrids. A male horse and a female donkey will give birth to a Hinny, while a female horse and a male donkey will give birth to a Mule.

The same goes for tigers and lions, male lion and a female tigress will give birth to a Liger, while a male tiger and a female lioness mating will result in a Tiglon

I thought that the only difference between the male and female reproductive cell's DNA code is the X-Y chromosome that determines gender, not differences that can define the species of the offspring.

Why does this happen? Justify it.