Figure 2

Effects of deviations from neutrality on gene genealogies. (A) Neutral evolution. (B) Population growth. (C) Population bottleneck. Here, only one ancestral lineage passes through the bottleneck, leading to a short tree with relatively long external branches. (D) Population subdivision. An initial population (represented by solid lines) separates into two subpopulations, which are denoted by dashed and solid lines. (E) Positive selection. An advantageous allele (represented by the dashed lines) sweeps through the population to fixation. Note that the genealogy of a selective sweep is similar to that produced by a population growth or bottleneck. (F) Balancing selection. An allele that is advantageous only in the heterozygous state (dashed line) appears in the population and is maintained at an intermediate frequency. Note that the genealogy under balancing selection is similar to population subdivision. N_e, effective population size.