SIGNATURE OF ANCIENT POPULATION-GROWTH IN A LOW-RESOLUTION MITOCHONDRIAL-DNA MISMATCH DISTRIBUTION

A mismatch distribution is a tabulation of the number of pairwise diff erences among all DNA sequences in a sample. In a population that has been stationary for a long time these distributions from nonrecombinan t DNA sequences become ragged and erratic, whereas a population that h as been growing generates mismatch distributions that are smooth and h ave a peak. The position of the peak reflects the time of the populati on growth. The signature of an ancient population expansion is apparen t even in the low-resolution mtDNA typings described by Merriwether et al. (1991). The smoothness of the mismatch distribution, an indicator of population expansion, is hardly affected by population structure, whereas mean sequence divergence increases in a pooled sample from hig hly isolated subpopulations.