Adaptive evolution of the tumour suppressor BRCA1 in humans and chimpanzees


Mutations in BRCA1 (ref. 1) confer an increased risk of female breast cancer2. In a genome-wide scan of linkage disequilibrium (LD), a high level of LD was detected among microsatellite markers flanking BRCA1 (ref. 3), raising the prospect that positive natural selection may have acted on this gene. We have used the predictions of evolutionary genetic theory to investigate this further. Using phylogeny-based maximum likelihood analysis of the BRCA1 sequences from primates and other mammals, we found that the ratios of replacement to silent nucleotide substitutions on the human and chimpanzee lineages were not different from one another (P=0.8), were different from those of other primate lineages (P=0.004) and were greater than 1 (P=0.04). This is consistent with the historic occurrence of positive darwinian selection pressure on the BRCA1 protein in the human and chimpanzee lineages. Analysis of genetic variation in a sample of female Australians of Northern European origin showed evidence for Hardy-Weinberg (HW) disequilibrium at polymorphic sites in BRCA1, consistent with the possibility that natural selection is affecting genotype frequencies in modern Europeans. The clustering of between-species variation in the region of the gene encoding the RAD51-interaction domain of BRCA1 suggests the maintenance of genomic integrity as a possible target of selection.

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Figure 1: Distribution of variation along BRCA1.
Figure 2: Ratios of replacement to silent substitution (ω) estimated for the indicated branches of the primate phylogeny.

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We thank Y. Zhang and B. Whittle for technical assistance; P. Board and C. Goodnow for comments on an early version of this manuscript; D. Easton and D. Goldgar for comments regarding previous studies; and the other researchers in the Australian Breast Cancer Family Study who contributed to this work, C. Andersen, K. Jennings, S. Brown, L. Porter, G. Dite and J. Maskiell.

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Correspondence to Gavin A. Huttley.

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the Australian Breast Cancer Family Study

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Huttley, G., Easteal, S., Southey, M. et al. Adaptive evolution of the tumour suppressor BRCA1 in humans and chimpanzees. Nat Genet 25, 410–413 (2000).

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