Begun and Aquadro 1992

Citation

Begun, D. J., & Aquadro, C. F. (1992). Levels of naturally occurring DNA polymorphism correlate with recombination rates in D. melanogaster. Nature, 356(6369), 519.

Links

• https://www.nature.com/articles/356519a0
• http://hawaiireedlab.com/pdf/b/begunandaquadro1992.pdf (internal lab link only)

Published Abstract

TWO genomic regions with unusally low recombination rates in Drosophila melanogaster have normal levels of divergence but greatly reduced nucleotide diversity1,2, apparently resulting from the fixation of advantageous mutations and the associated hitchhiking effect3,4. Here we show that for 20 gene regions from across the genome, the amount of nucleotide diversity in natural populations of D. melanogaster is positively correlated with the regional rate of recombination. This cannot be explained by variation in mutation rates and/or functional constraint, because we observe no correlation between recombination rates and DNA sequence divergence between D. melanogaster and its sibling species, D. simulans. We suggest that the correlation may result from genetic hitch-hiking associated with the fixation of advantageous mutants. Hitch-hiking thus seems to occur over a large fraction of the Drosophila genome and may constitute a major constraint on levels of genetic variation in nature.

Notes

The essential result is summarized in these two figures.

Under the neutral theory diversity within a species is expected to be 4Nμ (N is the population size) and divergence between species is expected to be 2tμ (t is the time of divergence in generations). Both of these are proportional to the mutation rate μ. Under a simple model 4N and 2t are not expected to change among loci. However, the mutation rate, μ, can easily change among different genes but the effect on both diversity and divergence is expected to be proportional. The authors found that diversity within a species increases with rates of recombination along a chromosome, but divergence between species does not. This is not consistent with the neutral theory and indicates some form of selection is shaping levels of genetic variation within species. The big question is what kind of selection. Both Hitchhiking from Selective Sweeps and Background Selection can contribute to this pattern and are not mutually exclusive.