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Published in:
2011 | OriginalPaper | Chapter
Selection
Author : Alison Etheridge
Published in: Some Mathematical Models from Population Genetics
Publisher: Springer Berlin Heidelberg
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In Remark 2.18 we introduced the notion of
nucleotide diversity
– the proportion of nucleotides that differ between two randomly chosen sequences. Its expected value is θ = 4
Neμ
(for a diploid population) where μ is the mutation probability per base pair per individual per generation and
N
e
is the effective population size. The mutation rate can be estimated directly (or from the divergence between species with a known divergence time) and this gives an estimate of
N
e
(Barton et al. (2007), p.426). This approach yields
N
e
~ 106 for
Drosophila melanogaster
, far lower than the actual (census) population size or indeed than the population size is likely to have been in the past. Moreover, although genetic variation is certainly higher in more abundant organisms, the relationship is rather weak. For example there’s only about a factor of ten difference between
Drosophila melanogaster
and humans. Abundant species have much less genetic diversity than expected from the neutral theory,
something else is going on
.