Combining sperm typing and LD analyses reveals differences in selective pressures or recombination rates across human populations

A previous polymorphism survey of the type 2 diabetes gene CAPN10 identified a segment showing an excess of polymorphism levels in all population samples coinciding with localized breakdown of linkage disequilibrium (LD) in a sample of Hausa from Cameroon, but not in non-African samples. This raised the possibility that a recombination hotspot is present in all populations and we had insufficient power to detect it in the non-African data. To test this possibility, we estimated the cross-over rate by sperm typing in five non-African men; these estimates were consistent with the LD decay in the non-African, but not in the Hausa data. Moreover, re-sequencing the orthologous region in a sample of Western chimpanzees did not show either an excess of polymorphism level or rapid LD decay, suggesting that the processes underlying the patterns observed in humans operated only on the human lineage. Taken together, these results suggest that either 1) a new hotspot of recombination has recently arisen on the human lineage and has reached higher frequency in the Hausa than in the non-African populations, or 2) there is no elevation in cross-over rate in any human population, and the observed variation results from long-standing balancing selection.

Key Words: balancing selection, diabetes, recombination hotspot

Online ISS 1091-6490
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