View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

Understanding how genetic variation is maintained is a major problem in population genetics. A variety of factors have been implicated to explain the maintenance of genetic variation in some contexts (e.g. balancing selection), but the potential role of epigenetic regulation to influence population dynamics has been understudied. It is well recognized that epigenetic regulation, including histone methylation, small RNA expression, and DNA methylation, helps to define differences between cell types and facilitate phenotypic plasticity. In more recent years, empirical studies have shown the potential for epigenetic regulation to also be heritable for at least a few generations, raising the possibility that differences in epigenetic regulation can act alongside genetic variation to shape evolutionary trajectories. Like genetic mutation, heritable differences in epigenetic regulation can arise spontaneously; these are termed ‘epimutations’. Epimutations differ from genetic mutations in two key ways – they occur at a higher rate, and the loci at which they occur often revert back to their original state within a few generations. Here, I present an extension of the standard population-genetic model with selection to incorporate epigenetic variation arising via epimutation. My model assumes a diploid, sexually reproducing population with random mating. In addition to spontaneous genetic mutation, I included parameters for spontaneous epimutation and back-epimutation, allowing for four potential epialleles at a single locus (two genetic alleles, each with two epigenetic states), each of which affect fitness. I then analyzed the conditions under which stable epialleles were maintained. My results show that, for certain sets of parameters, epimutations affecting fitness can facilitate the maintenance of recessive deleterious alleles that would otherwise be purged from the population. This demonstrates that heritable epigenetic regulation that itself is maintained only a few generations may be an important factor in the long-term maintenance of genetic variation in populations.

Heritable epigenetic variation facilitates maintenance of genetic variation