Thanks, I was particularly impressed to read about Aborigines flowing strict rules of marriage to avoiding getting themselves wiped out in the harsh climate. They can trace their DNA thru hundreds of years to the same location but they are careful how they remain pure yet not allow inbreeding.
You are welcome . Yes you are right about the aborigines .
Breeders of purebred livestock have introduced a term, linebreeding, to cover the milder forms of inbreeding. Exactly what the differences is between linebreeding and inbreeding tends to be define differently for each species and often for each breed within the species. inbreeding at its most restrictive applies to what would be considered unquestioned incest in human beings for example parent to offspring or a mating between full siblings. Uncle-niece, aunt-nephew, half sibling matings, and first cousin matings are called inbreeding by some people and linebreeding by others.
What does inbreeding (in the genetic sense) do? it increase the probability that the two copies of any given gene will be identicals and derived from the same ancestor. Technically, the animal is homozygous for that gene. The heterozygous animal has some differences in the two copies of the gene Remember that each animal (or plant, for that matter) has two copies of any given gene (two alleles at each locus, if you want to get technical), one derived from the father and one from the mother. If the father and mother are related, there is chance that the two genes in the offspring are both identical copies by the common ancestor. This is neither good nor bad in itself. Consider, for instance, the gene for PRA (progressive retinal atrophy), which causes progressive blindness. Carriers have normal vision, but if one is mated to another carrier, one in four of the puppies will have PRA and go blind. Inbreeding will increase both the number of affected dogs (bad) and the number of genetically normal dogs (good) at the expense of carriers. Inbreeding can thus bring these undesirable recessive genes to the surface, where they can be removed from the breeding pool.
Unfortunately, we cannot breed animals based on a single gene the genes come as a package. We may inbreed and rigorously remove pups with PRA or even their parents and littermates from the breeding pool. But remember inbreeding tends to make all genes more homozygous. In at least one breed, an effort to remove the PRA-causing gene resulted in the surfacing of a completely different and previously unsuspected health problems . It is easier and faster to lose genes (sometimes very desirable genes) from the breeding pool when inbreeding is practiced than when a more open breeding system is used. In other words, inbreeding will tend to produce more nearly homozygous animals, but generally some of the homozygous pairs will be "good" and others will be "bad".