Sims baby Wrong Genetics

Hi All- 

Every time my two sims try to have a baby they will end up with genetics that don't match theirs. ( For Example: Both blonde with blue eyes- having children with black hair and dark brown eyes). After 5 or 6 children I have just gave up for now, but I would like a solution. I did try with another set of parents and it does the same thing. Any ideas on fixing this?? 

Thanks!