Detecting selection-induced departures from Hardy-Weinberg proportions

Joseph Lachance

doi:10.1186/1297-9686-41-15

Abstract

Viability selection influences the genotypic contexts of alleles and leads to quantifiable departures from Hardy-Weinberg proportions. One measure of these departures is Wright's inbreeding coefficient (F), where observed heterozygosity is compared with expected heterozygosity. Here, I extend population genetics theory to describe post-selection genotype frequencies in terms of post-selection allele frequencies and fitness dominance. The resulting equations correspond to non-equilibrium populations, allowing the following questions to be addressed: When selection is present, how large a sample size is needed to detect significant departures from Hardy-Weinberg? How do selection-induced departures from Hardy-Weinberg vary with allele frequencies and levels of fitness dominance? For realistic selection coefficients, large sample sizes are required and departures from Hardy-Weinberg proportions are small.

Highlights

Natural selection modifies the probabilities that alleles are found in either homozygous or heterozygous form
When viability selection results in significant departures from Hardy Weinberg (DHW), the genetic footprint of natural selection can be observed in sequence data [13]
Magnitude of selection-induced departures from HardyWeinberg proportions The sign and magnitude of selection-induced departures from Hardy-Weinberg are determined by allele frequencies and fitness dominance

Summary

Introduction

Natural selection modifies the probabilities that alleles are found in either homozygous or heterozygous form. When the assumptions of the Hardy-Weinberg principle are violated, such as when viability selection is present, this result cannot be expected to hold. While this has been known for decades, many current studies assume Hardy-Weinberg proportions (p2 : 2pq : q2) without explicitly considering the impact of selection. Tests of Hardy-Weinberg proportions have been used to detect genotyping errors [4,5,6]. It is an open question whether natural selection confounds such tests. One can ask: When does natural selection result in significant departures from Hardy-Weinberg proportions?

Methods

Results

Conclusion