population expansion
Sousa V, Peischl S & Excoffier L 2014 Impact of range expansions on current human genomic diversity. Curr Opin Genet Dev 29:22-30.
- gene surfing can occur on standing variation, and it is not restricted to neutral mutations
- it is not restricted to neutral mutations
- mutations evolve almost neutrally at the front of expanding populations because drift is so strong
- because deleterious mutations happen more frequently than beneficial ones, deleterious mutations should thus accumulate by gene surfing in the genome during range expansions and create an expansion load
- expansion load created during range expansions could explain the observation of an overall higher proportion of damaging mutations in non-African populations
- the analysis of protein coding genes from 2440 individuals of European and African descent revealed that 86% of the SNPs had alleles with a frequency less than 0.5%
- this excess of singletons/doubletons as compared to the expectation in a stationary population had not been suspected in former studies bearing on smaller sample sizes
- these rare variants are now thought ... to be partly responsible for the missing heritability paradox
- how can population growth explain the counterintuitive observation of an excess of rare functional variants?
- this apparent paradox is resolved by realizing that human populations went first through a bottleneck and are currently growing, without having reached equilibrium yet
- as the population size increases, more mutations enter the population, including more deleterious mutations
- even though the efficacy of selection increases during the growth phase, the proportion of sites with deleterious mutations also increases before a new equilibrium is met
- population growth after a bottleneck should result in a transient excess of rare functional variants
- range expansion models differ in important aspects from models of pure demographic growth
- the interplay between selection and demography is different in the two models
