Positive Selection on Genes in Humans as Compared to Chimpanzees

Abstract

Positive selection has been identified and extensively studied in many human genes. In contrast, positive selection in the closest human relative, chimpanzee, has been largely unstudied until recently. With the complete sequencing of the human and chimpanzee genomes, a comparison of the types and numbers of genes that underwent positive selection in the two species is possible. The types of genes under positive selection in human and chimpanzee are different with regard to gene function, but no particular type accounts for a large part of this difference. However, significantly more genes experienced positive selection in the chimpanzee lineage than in the human lineage.

Keywords: positive selection; human; chimpanzee; molecular evolution; population size

Figure 1.

Functional differences between human and chimp unshared positively selected genes (PSGs). Human and chimp PSGs show a significantly larger difference in distribution across (a) biological process groups and (b) molecular function groups than by chance (P=0.84% and 0.26%, respectively; one‐tail randomization test). The 373 unshared human and chimp PSGs were randomly divided into 147 human PSGs and 226 chimp PSGs and χ2 was computed. This procedure was repeated 10 000 times to obtain the null distribution of χ2. The bars show the frequency distribution of the χ2 values in the random divisions and the arrows show the observed χ2 values. Here the randomization test is superior to the standard χ2 test because the functional groups are not independent from one another and a single gene may belong to more than one group. Similar results are obtained when the seven shared PSGs are included. (c) Biological process and molecular function groups show the greatest differences between human and chimp unshared PSGs, as ranked by individual χ2 values. Shown here are the groups that each contributes at least 2% of the total χ2 of all groups. Groups with a higher frequency of human PSGs than chimp PSGs are in red, whereas those with a higher frequency of chimp PSGs than human PSGs are in blue. Reproduced from Bakewell et al..

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Bakewell, Margaret A, and Zhang, Jianzhi(Jul 2008) Positive Selection on Genes in Humans as Compared to Chimpanzees. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020856]