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The Impact of Population Expansion and Mutation Rate Heterogeneity on DNA Sequence Polymorphism

Summary: The Impact of Population Expansion and Mutation Rate Heterogeneity on
DNA Sequence Polymorphism
Stkphane Ark-Brosou* and Laurent ExcofJer"f
*Institut National Agronomique Paris-Grignon, France; and tGenetics and Biometry Laboratory, Department of Anthropology,
University of Geneva, Switzerland
In order to study the effect of mutation rate heterogeneity on patterns of DNA polymorphism, we simulated samples
of DNA sequences with gamma-distributed nucleotide substitution rates in stationary and expanding populations.
We find that recent population expansions and mutation rate heterogeneity have similar effects on several poly-
morphism indicators, like the shape and the mean of the observed pairwise difference distribution, or the number
of segregating sites. The inferred size of population expansion thus appears overestimated if nucleotides have
dissimilar substitution rates. Interestingly, population expansion and uneven mutation rates have contrasting effects
on Tajima's D statistic when acting separately, and the consequence on the associated test of selective neutrality is
investigated. The patterns of polymorphism of several human populations analyzed for the mitochondrial control
region are examined, mainly showing the difficulty in quantifying the respective contribution of past demographic
history and uneven mutation rates from a single sampled evolutionary process. However, substitution rates appear
more heterogeneous in the second hypervariable segment of the control region than in the first segment.
New molecular data are providing information that
is qualitatively different from that previously available,
as the number of evolutionary steps separating a given


Source: Aris-Brosou, Stéphane - Department of Biology, University of Ottawa


Collections: Biology and Medicine