Correct females don't express it. Its probably not a popular opinion because most say they carry it sight unseen so its impossible to breed out without test breeding.
It happens because of the shredder/fray gene associated with lavender reacting with the wing patch of duckwing males. Shredder issues do show on females and if you breed that out you're breeding out the wing patch issue.
When I had it I looked at it as one in the same and breed to get rid of it as a whole not separate issues.
It pretty much shows as soon as the males feather in in that area. The feathers just don't develop and stay like pin feathers. It does become more obvious the older they get.
It's much less noticeable, but when I compare my Isabella hens to my Brown hens, I can definitely tell that the lav girls have fray, but there's no way to tell if they carry wing patch. I personally do not believe they are always necessarily linked.
It absolutely IS possible to breed out, but I guess I'm one of those that believe it will require test breeding. Are you saying you don't feel that's true? Have you managed to eliminate wing patch, fray, or both? I am breeding my isabellas to light and dark browns from Bud Blankenship this year. I have an Isabella cock out there that I've kept around, undecided as to whether or not to breed him. I know his sisters that I'm breeding to brown cocks carry the same genes he does, but it's really hard throwing such an ugly bird in there with those beautiful brown pullets!
What I guess I could do is breed him to the brown pullets, and then breed the split offspring from the two pens together (Is. cock over br. hens x br. cock over is. hens) to get my lavenders, then go back to the good brown stock for more splits. There actually ARE things I like about the Isabella line I have! I think they have lovely toplines and they lay very large (albeit tinted) eggs—actually much larger than the browns. They are large birds, too, bigger than the standardbred browns which is not necessarily good. They lack width. I haven't nailed strong yellow legs yet, either, but they aren't stark white so that's something.
I'm aiming for at least three crosses back to Bud's browns and then I'll be separating the Isabella's completely, breeding lav to lav only, and working on eliminating feather quality defects. After that, I'll be able to refocus on type and pattern. Pattern problems aren't as visible in Is females as browns, but there's still things like bricking, mossyness, and shafting to worry about eventually. I'd like to have something of decent quality to show within 2-3 years, even if only females. Is anyone showing Isabellas to represent the variety anywhere? I'd love to talk.