Question

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

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

I thought that the only difference between the male and femalereproductive cell's DNA code is the X-Y chromosome that determinesgender, not differences that can define the species of theoffspring. Why does this happen?