Haplogroup - Haplogroup Population Genetics

Haplogroup Population Genetics

It is usually assumed that there is little natural selection for or against a particular haplotype mutation which has survived to the present day, so apart from mutation rates (which may vary from one marker to another) the main driver of population genetics affecting the proportions of haplotypes in a population is genetic drift — random fluctuation caused by the sampling randomness of which members of the population happen to pass their DNA on to members of the next generation of the appropriate sex.

This causes the prevalence of a particular marker in a population to continue to fluctuate, until it either hits 100%, or falls out of the population entirely. In a large population with efficient mixing the rate of genetic drift for common alleles is very low; however, in a very small interbreeding population the proportions can change much more quickly. The marked geographical variations and concentrations of particular haplotypes and groups of haplotypes therefore witness the distinctive effects of repeated population bottlenecks or founder events followed by population separations and increases.

The lineages which can be traced back from the present will not reflect the full genetic variation of the older population: genetic drift means that some of the variants will have died out. The cost of full Y-DNA and mtDNA sequence tests has limited the availability of data; however, their cost has dropped dramatically in the last decade. Haplotype coalescence times and current geographical prevalences both carry considerable error uncertainties. This is especially troublesome for coalescence times, because most population geneticists still continue (albeit decreasing a little bit) to use the "Zhivotovski method", which is heavily criticised by DNA-genealogists for its falsehood.