Why can't mules have offspring?

Question

What is the real cause for them being sterile?

Answer 1

Mules are a hybridized species. They are a mix of a horse and a donkey. Hybrids are generally sterile because of differences in the chromosomes of the parents. The chromosomal difference came about from the divergence of the two species millions of years ago.

Answer 2

here's a website that explains it well:

http://www.biolbull.org/cgi/content/abst...

Answer 3

It has to do with chromosome numbers.

Horses have 64 chromosomes and therefore make gametes with 32 chromosomes.  Donkeys have 62 chromsomes and make gametes with 31.  So, mules end up with 63 chromosomes.  When the mule's s*x cells attempt to go through meiosis, the odd number of chromosomes creates a problem because there aren't equal pairs.  This means that the mule can't make viable gametes.