This may be complete ignorance, but I think you are taking this genetic traits thing the wrong way. As long as two things are in the same Animalia (mammal, reptile, etc.) and they have the same number of chromosomes, then an egg can theoretically be made. Of course, the only problem would be weather the females body would accept the sperm. The way i see it these races are just like the human races (Hispanic, African American, Caucasion, Etc.); so unless you (the devs) want to change each race into a species, then diversify these species into races (once again, like humans), then the interbreeding should be possible, and would be a very neat thing within the game indeed. However, if you want to allow interbreeding, you would have to make sure that it is as much like real life as possible, which means providing every trait possible, then randomization as in real life, so that it would be accepted as a liked improvment. If this exactness did not happen, then everyone would soon find out the most beneficial combiniation of genes, and would spread the knowledge, and the improvement would have been deemed nearly useless. Of course, I may just be the holder of complete ignorance on this...