Deleterious hitchhiking and the cost of balancing selection Mutations within genomes are subject to various evolutionary pressures. One of these is balancing selection, where genetic variants are maintained at intermediate frequencies. This type of selection underlies several evolutionary-important genetic regions, including those relating to immunity and mating-type specification. However, linked variants in their vicinity can also spread with the balanced mutation. These include weakly-selected deleterious mutations, the presence of which can create a cost to natural selection. Such an enrichment of deleterious variants has been observed in genome data, but we lack a general model of how likely deleterious mutations can be captured by balancing selection. In this talk, I will present ongoing work from my group where we develop a branching-process model to calculate the probability that deleterious variants spread with balancing selection, and also calculate the time they persist in the population. These models will inform on how regions of the genome interact and what costs of natural selection arise due to selection acting on linked sites. This article was published on 2026-01-27
