Read this one slowly, maybe a couple of times, but once you grab it, it will be like an ah-ha moment.
One of the best little tidbits, probably the single best, in the book Start Where You are with What You Have, a book that Bob recommended a few years back and which I was finally able to get a copy of, is that:
breeding poultry is ultimately maintaining a strain an flushing out all of the negative recessives while fixing the positives
Eliminating negative and fixing positive dominant traits is fairly straightforward. They're easy to get rid of, and they're easy to hold onto. It's all of the various recessive genes that are harder to deal with and for which you have to go fishing. As you maintain a strain, the birds become more and more unified genetically. As this happens they share in common the many traits which were more individually dispersed among their forebears. As more birds come to share recessive genes, there is an increased likeliness that progeny will manifest phenotypically a trait that was beforehand hidden deep in the genetic code of some of their ancestors. That quality might be positive; that quality might be negative. As one continues to maintain a strain, these traits will emerge; it then requires a little bit of genetic savvy to know how to eliminate them, if they are negative traits.
It is important to recognize the difference between maintaining a strain with a pedigree of related birds, i.e. birds of a clan versus breeding higgledy-piggledy without records and ending up pairing siblings indiscriminately and other such folly, which causes too many negative recessives to emerge at once creating a great big mess of negative traits.
So, as one is maintaining a, broadly speaking, inbred clan, which we call a strain, one is constantly selecting for vigor and health as well as breed specific positive traits while flushing out and culling for the many negative recessives which emerge.
Now, say one begins to inbreed and after so many years a deformity arises, what can be done?
Well, one typical response is to panic and to bring in new blood. What happens in this scenario is that the resultant heterogeneity introduced by the new blood causes the flushed out gene to recess; ergo, it goes back into hiding. One might think, "Oh thank God for that new blood", but one hasn't eliminated the trait; it is still there; it is merely in hiding, as it was before. If one continues to breed, it will emerge again. On the other hand, introducing the new blood, has also introduced into the mix a whole host of new recessives, which over time will have their chance to emerge as well. Thus, it's a quick fix but a compounded problem. Moreover, the flock has, at this point, lost the coveted, standard-based uniformity it was beginning to achieve.
On the other hand, breeding is about cultivating an ever deepened awareness. This is why mentors and show attendance are so very necessary for becoming an excellent breeder. There are so very many traits of which one must be aware. If a negative recessive emerges, and if it is not caught, meaning if it is not perceived and culled, and then if those birds are then bred from, the result will be a strengthening of that recessive in the phenotype, i.e. one starts to see more and more birds with the deformity. If this is allowed to go on for too long such that one's flock becomes homozygous for a recessive trait, we say that the trait is "locked in" or "fixed", which means that the only way to get rid of it is to actually bring in new blood that is able to first mask it and then as it begins to reappear, which it eventually will, one will have the sense to recognize it and to cull for it accordingly.
So the trick is not to cover up the recessives but to know how to get rid of them. For this, one uses the progeny test.
To promote understanding, in order for a recessive trait to emerge visibly a chick must receive that gene from both parents. So, only if both parents have that gene will it emerge.
Thus, for a progeny test, on takes the bird, or birds, with the deformity and breeds them to birds that appear to lack the deformity. Then, one hatches the eggs from specific pairings and keeps meticulous track of who's who. It is important to hatch enough chicks, perhaps a couple of dozen, in order to have a large enough control group. NB: These chicks are not meant to become breeders; all of these chicks are destined to be culled from the flock because every single one of them will have the negative gene regardless of whether or not it is visible. Now, as they develop, some the chicks from some pairings will exhibit the negative recessive trait, while other pairings will not. What this means is that in the breedings where some of the chicks--not all, but some--are manifesting the recessive trait, that trait is present in both parents, the one that visibly possesses the trait as well as in the parent that does not visibly (phenotypically) appear to have it. That seemingly innocent parent is a carrier; even though it appears not to have it, it will disperse the trait throughout the flock and must be culled.
Then, among other test matings, there will be groups in which none of the chicks manifest the negative trait, assuming the control group is large enough (two dozen chicks as opposed to only three chicks) one can assume that the parent, who does not appear to have the negative trait, actually does not. This parent is then saved for future breeding.
Only these parents are allowed to move forward, these parents who, when paired with a bird that visibly manifested the negative trait, threw no chicks with that trait. They can be assumed to be clean of that trait. All other breeders are then culled, and only these birds are used moving forward. Your flock will then be clean of the negative gene.
Thus inbreeding allows us to draw to the fore and maintain all of the hidden positive recessives that are needed for an excellent bird, and it allows us to concentrate in our flocks a high level of good things, including vigor and disease resistance. On the other hand, inbreeding also allows us, whether we like it or not, to flush out the latent negatives and then, through the art and science of breeding, to eliminate them.
Thank you for the tips! I will go search out the books you mentioned.
