Hmm... so basically you are line breeding so that you can see whether there are recessive genes that cause genetic illnesses?
I guess I was thinking that when two related cats had kittens, there would always or almost always be such genetic problems; so, I figured, why do you do it? It wouldn't make any sense if there were so many that you had to retire just about every cat you bred... but you're saying that there aren't that many, right?
I'll admit I understand genetics well enough, but their practical application in breeding is something I've never really studied. When you encounter genetics in biology class, you are given rather isolated sets of traits--blue eyes, brown eyes, green eyes; red, pink, and white flowers; and so on--but when you are breeding cats you have a huge amount of genetic information being passed on to each kitten, and interacting; and you don't know what's being passed on unless it's dominant or unless the kitten has two recessive genes... So it's like trying to figure out what's inside the black box. High school biology doesn't really get into that much. :P