Donkeys and wild equids have a different number of chromosomes (a donkey has 62 chromosomes, a domesticated horse 64, and the zebra, depending on the species, has 32-46 chromosomes), but the hybridization of both of these species is possible.
That is crazy that they can create offspring at all. Does anyone know how that works? From my High School biology, you need to pair up each chromosome from the father and the mother. What happens when there isn't the same number?
