heres another imo from breeding fish and a few other things. inbreeding for traits its acceptable to breed mother to son son to daught but not brother to sister. idea being if there is a recessive trait it is almost 100% siblings are carriers resulting in deformation. but much less likely that one parent and one offspring out of hundreds will carry negative recessive but usually the positive traits are something visual so you cant know for sure. IDK if it makes sense how I explain it but thats the jist of it