Self-fertilization sweeps up variation in the worm genome

Abstract

A new study reports a comprehensive survey of genetic diversity in natural populations of the nematode Caenorhabditis elegans. Their analyses suggest that recent chromosome-scale selective sweeps have reduced C. elegans genetic diversity worldwide and strongly structured genetic variation across its genome.

Figure 1

Influence of a self-fertilizing mating system on the patterns of genetic variation across the genome. When a new advantageous mutation (red) arises against a backdrop of already pre-exisiting genetic variation on the rest of the chromosome (other colors; A), it will increase in frequency under natural selection (B). Under outcrossing (left), recombination during sexual reproduction will tend to mix genetic markers at other sites until the genetic backgrounds are more uniformly distributed (B). Under self fertilization (right), recombination still occurs, but is less effective because the paired chromosomes tend to be genetically identical to one another (B). Thus, under outcrossing, scanning the pattern of sequence variation across the genome would be expected to identify localized regions of low sequence variation at sites undergoing selective sweeps (C, left), whereas the a similar analysis under self fertilization would be expected to identify an overall pattern of reduced genetic variation (C, right), providing less information about the specific genetic target of natural selection.