The above posters have it right but still in a small way wrong. Line breeding is any breeding program that focuses on a single parent or small set of parents repeatedly crossing and intercrossing the offspring. Whether it is parent to offspring or grandparent to offspring, or half siblings, it is still considered line breeding. The key is that no external genetics are brought into the breeding program. Focus on those three words: "no external genetics".
Line breeding has negatives such as concentrating deleterious genes, narrowing the genetic base, and covering up recessives with homozygous dominant genes. Positives are that it permits very rapid stabilization of desired traits, permits weeding out of undesired genetics, and is a very viable breeding method where chickens are concerned.
Don't get me started on mass selection, round robin breeding, breeding pools, or closed breeding populations. I am using a closed breeding population with my Silver Laced Wyandottes that lay blue eggs. This just means that there is enough genetic diversity that it is technically not line breeding, but it is still a closed population with no more external genetics coming in.
Line breeding has negatives such as concentrating deleterious genes, narrowing the genetic base, and covering up recessives with homozygous dominant genes. Positives are that it permits very rapid stabilization of desired traits, permits weeding out of undesired genetics, and is a very viable breeding method where chickens are concerned.
Don't get me started on mass selection, round robin breeding, breeding pools, or closed breeding populations. I am using a closed breeding population with my Silver Laced Wyandottes that lay blue eggs. This just means that there is enough genetic diversity that it is technically not line breeding, but it is still a closed population with no more external genetics coming in.
