Abstracts

Human Genome Diversity

Genetic distances play an important role in estimating divergence time between bifurcated populations. However, their interpretation can be greatly complicated by demographic processes, such as migration and population dynamics. As a rule, genetic distances assume constant population size, no gene flow, and mutation-drift equilibrium. When these assumptions fail, estimates of divergence time may be far away from their actual values. As an example, the widely used distance (δμ)2, based on microsatellite variation (Goldstein et al. 1995), underestimates divergence time if two diverged populations are growing in size or connected by gene flow. We suggest a different estimator of population separation time based on a microsatellite statistic, TD, that does not assume mutation-drift equilibrium, is independent of population dynamics in the absence of gene flow, and is robust to weak migration flow for growing populations (Zhivotovsky 2001). However, it requires knowledge of microsatellite variation (the variance in the number of repeats) at the beginning of population separation. A few approaches are suggested to overcome this problem, and applied to data on variation at autosomal STR loci with di-, tri-, and tetranucleotide repeats in worldwide populations. TD gives the lower and upper bounds of 57 and 135 thousand years, respectively, for separation of the Out-of-Africa branch of anatomically modern humans from Africans. The data also suggest that the Asian and European populations diverged from each other about 20 thousand years later after occurrence of the Out-of-Africa branch (Zhivotovsky 2001).

Literature.
Goldstein, D. B., A. R. Linares, L. L. Cavalli-Sforza, and M. W. Feldman. 1995. Genetic absolute dating based on microsatellites and the origin of modern humans. Proc. Natl. Acad. Sci. 92: 6723-6727.
Zhivotovsky, LA. 2001. Estimating divergence time with use of microsatellite genetic distances: impacts of population growth and gene flow. Mol. Biol. Evol. 18: 700-709.

Note. Abstracts are published in author's edition

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