Genetics and Breeding

Inbreeding is the mating of closely related animals to increase homozygosity within a population. Common alleles become more concentrated — the gene frequency increases in other words — and animals become more and more closely related with each generation. The reliability of high performing animals producing more high performing animals becomes very predictable. It sounds like the only breeding approach you’ll ever need, but there can be consequences. Outbreeding on the other hand increases heterozygosity by mating unrelated animals. New alleles are introduced and the gene pool widens. From this and the Hardy-Weinberg Equilibrium, it would appear that a breeding programme would go nowhere fast were it to rely solely on outbreeding. Yet there can be benefits. more »

Outbreeding (also called crossbreeding) is the opposite of inbreeding, in that unrelated animals are mated with the effect of increasing heterozygosity. Let’s step through an example by starting with two unrelated populations, 1 and 2. Population 1 has gene frequencies at the A locus of p1 = 0.8 and q1 = 0.2. Population 2 has gene frequencies at the A locus of p2 = 0.1 and q2 = 0.9. Right away we can tell the two are unrelated as the gene frequencies differ so much. Now cross them to create an F1 generation. (Back in Explaining Mendel’s Results Visually we defined an F1 generation as one resulting from the crossing of two purebred populations. Here we are using it more broadly to include two unrelated, but not necessarily purebred, populations.) more »