AAM, thanks for the info on the lethal white thing with the cat post.
Do you think this sort of thing happens because of so much in breeding breeding for a certain trait, such as for paint, and taillessness?
That's too bad if so. I think breeding should be for overall, and not so much for 1 certain trait. I know around here there are alot of paints who have some really bad confirmation flaws. Mostly very short necks. There are alot of backyard breeders around here, and they all seems to want paint, and as long as they get that, they think they've done good:) I've seen some pretty bad confirmation paints but people still comment "isn't he/she pretty" and I'm thinking "what are you looking at:)" I was guilty of not being able to see past color before. It was when I started looking at horses, that I didn't particularly like the color, but still the horse was pretty that I learned it's more to do with confirmation then color that makes a pretty horse.
Becky
I didn't answer your question very well, you are correct in that all these different patterns are just being recognized because of all the cross breeding of the colors. The lethal white syndrome is just because overos carry a gene that causes lethal white, if you breed two carriers together you can get a lethal white.
My genetics book says that crossing the different patterns destroys the integrity of each marking, that's why professional breeders don't do it.
So any nasty alleles that are linked to the particular trait you're breeding for will also be concentrated. If the trait you're breeding for doesn't have any nasties directly linked, you're home free. If they are NOT linked but just happened to be in the gene pool, they will gradually breed out.
An example would be the Siamese color, which is a recessive but isn't directly linked to any nasties. On the other hand, the crossed eyes in Siamese ARE linked to a visual defect, which is one reason the breeders have been doing their best to eliminate crossed eyes. They've done a pretty good job, you don't see anywhere near as many cross-eyed Siamese as you used to. But of course they still have blue eyes and the coat pattern. Same thing goes for the kinked tails, but as far as I know the kink (unlike the taillessness in Manx) wasn't linked to anything, the judges just didn't like it.
The problem arises when something like the lethal white or Manx tail is in the very same genetic information that produces the desired trait. In the old days, you had to figure out by trial and error which horses (or cats) were carriers and tended to throw the lethal. Now the DNA typing takes care of all that.