I would love it if (in combination with customisable exhibits) we could get reptile morphs, coat variations in different animals, slight colour differences in animals. I'd also love to be able to do research into animal genetics in game which you could do for a specific animal and could give a rough estimate of the chances of offspring getting certain things e.g. melanism, albinism, or different morphs that are possible for the various types of animals. It wouldn't have a huge effect on gameplay aside from lethal alleles (which, thinking about it, I'm surprised we don't have unsuccessful pregnancies in the game?) and would just be something that may alter the market or be a personal preference for someone.