rokimoto, or anyone, suppose i have a superior par uf chickens. by line breedingi should be able to recreate their original gene pool indefinatly.theoreticaly. but that couldnt mean the same exactly phenotypically. is this correct. also, i dont understand how prepotency enters the picture without line(in)breeding. i do know of several distinct breeds being created by the use of a prepotent male, also distinct lines within a breed. can a female also be prepotent, i wouldnt see ahy not, i just am not aware of that. thankyou. robb
Line breeding works because you inherit half (50%) your genes from each parent. So in the first mating the progeny get half their genes from their mother and half from their father. If you cross the progeny back to their parent the progeny already has half the genes that that parent has. So the progeny of that inbred cross inherit 75% genes from the superior parent and have only 25% of the genes from the other, now, grandparent. The extra 25% comes from the son or daughter. In the second backcross of the superior parent 87.5% of the genes in the resulting progeny come from the superior parent.
By Rokimoto on Saturday, January 5, 2002 - 11:57 pm:
This just means that you have a much better chance of getting something that looks like the superior parent by doing this. The problem is that the superior parent may be heterozygous (have two different copies (alleles) of the same gene) and will keep segregating these two alleles in all of their progeny. You will still be more likely to reproduce other aspects of the bird, but if what the bird looks like depends on being heterozygous the results can be pretty low.
Take a frizzled blue parent. It may not be worth your while to line breed. Ff+ Blbl+ are the show quality birds, but if you line breed only one quarter of the progeny will be both well frizzled and blue, so your progress will not be as good, but it may still be better than breeding any two show quality birds together because you end up with the same ratio.
If the prepotent bird is heterozygous for many genes it is very unlikely that you will get a bird exactly like it genetically even by line breeding.
Line breeding works best for what we call additive traits. Where genes add together. 3 good alleles are better than 2 and 4 are better than 3. If the superior parent has many good additive alleles, line breeding will allow you to put many of these back into the inbred progeny, but you aren't likely to recreate the exact genetics of the superior parent.
The problem is that any bad genes that the prepotent parent has increases in the progeny too.