Good articles. My knowledge in genetic science is quite limited. Thank you.
It is pretty basic, but this is the way I always saw it. The more I bred a species that were related, my cull rate went up. Though I usually become more selective with a single species over time; even from one single pair of the same generation; I would notice an increase in percentage on each generation further from the parents. However, in a lot of cases, I would also get offspring that were much more brilliant in color and fin structure (sometimes even size) than the original parents. This is where I would usually introduce an outside line. Best I found is to swap with another breeder.
I also noticed, and don't know if anyone else has had the same observation, that some of the CA/SA cichlids seem to be more likely to reject a potential mate if it is a sibling. Basically, if I put a boy and a girl in a tank together, the probability of rejection (or assassination) was higher if related than if not siblings. Africans never seemed to care.