But wouldn't dominance mean it'd be easier to breed around in poultry? Because a dominant gene can't help but express itself, and than you at least know what you're dealing with. Where as recessive genes can hide for generations, and pop out of the wood work when you pair certain birds/families and least expect it. A good reminder why test mating is so important though. Mammals are very different than avians, wow... My brain was not ready to look over that paper this morning Susan. lol Need more java, maybe more brain. haha
It is the incomplete penetrance that is the bugger. With incomplete penetrance, you can have an animal that carries the genetic makeup of the trait (genotype), but not display any, or only a very mild, symptom (phenotype). So, if cross beak is an incomplete penetrance, you could have a hen or a cockerel that carries the gene(s) for cross-beak, but neither one show it. You'd have no reason to test breed for it, because neither parent was showing any signs of it. The "good" thing about it being recessive is that, if one chick does show up as cross-beak, then you know both parents are carriers.
With a dominant trait, like TVD in Labs, neither parent could show any signs of it, but one parent could have the genetic makeup. If even one pup shows up with TVD - or even mild regurgitation, or murmur - then you know at least one of the parents has it. Since it only takes one to produce it (dominant), now you have to identify which parent is the source and with incomplete penetrance, you can breed a lot of pups before you produce another pup that shows signs of TVD. It is one of the heartbreaks in Labrador Retrievers.
As far as the paper goes - think how much coffee I needed to write that! lol