A new test suggests hundreds of amino acid polymorphisms in humans are subject to balancing selection

Abstract

The role that balancing selection plays in the maintenance of genetic diversity remains unresolved. Here, we introduce a new test, based on the McDonald–Kreitman test, in which the number of polymorphisms that are shared between populations is contrasted to those that are private at selected and neutral sites. We show that this simple test is robust to a variety of demographic changes, and that it can also give a direct estimate of the number of shared polymorphisms that are directly maintained by balancing selection. We apply our method to population genomic data from humans and provide some evidence that hundreds of nonsynonymous polymorphisms are subject to balancing selection. What maintains genetic variation remains an unresolved mystery. This study describes the development of a new test and its application to human population genomic data, suggesting that natural selection may have a much more important role than previously thought, with hundreds of non-synonymous polymorphisms subject to balancing selection.