Skip to main content
Figure 1 | Human Genomics

Figure 1

From: Genome-wide scans for loci under selection in humans

Figure 1

Coalescent representation of a neutrally evolving sequence. (A) Explicitly tracing the history of a sample of alleles from the population, each progenitor allele is derived from a randomly chosen parental allele. Occasionally, two progenitor alleles are derived from the same parent, causing the lineages of these two alleles to unite or coalesce when they are followed backward in time from the present. Note that if progeny are derived from parents at random, the probability that two lineages coalesce increases as the number of distinct lineages increases and as the effective population size decreases. Thus, for a constant-sized population, a characteristic distribution of waiting times between coalescent events is expected. (B) The untangled, coalescent representation of (A) is created by treating lineages as branches, ignoring the intermediate ancestors between coalescent events. Under neutrality, mutational events (represented by shaded diamonds) are uniformly distributed throughout time, hence the number of mutations that occur on a branch is proportional to the length of the branch. Note that mutations occurring on external branches are rare, appearing on only a single allele, whereas mutations occurring on internal branches are common.

Back to article page