Why is it impossible for certain creatures to breed with other creatures?

Question

lol just thought i throw this in...too cute hehe

http://www.gamertagpics.com/messages/Ghost_Dog_3/FUNNY%20Cat%20top%20of%20dog%20small.JPG

Answer 1

The most general reason is that for successful fertilization of the egg, the chromosomes from the male and female have to match up.  Because different species have a different number of chromosomes, or, if the same, they are arranged differently, the embryo won't be viable.

Other reasons are non-implantation of the fertilized egg, or rejection of the embryo as foreign by the mother.

Answer 2

The DNA and the chromosomes is the reason... think of it this way you can't take parts a car and parts from a tv and make a ferrari...