population expansion

Lohmueller KE 2014 The distribution of deleterious genetic variation in human populations. Curr Opin Genet Dev 29:139-146.

  • recent population growth results in an influx of new deleterious mutations into the population
  • selection has not yet had sufficient time to eliminate them
  • these variants also tend to be rare
  • recent population growth increases the per generation efficacy of selection to reduce the frequencies of pre-existing deleterious variants
  • these two effects tend to cancel to give the same genetic load in expanded and non-expanded populations
  • the average load may not have been affected by demography
  • the manner in which a particular population arrives at that load, however, is very dependent on demography
  • very rare variants (<0.05% frequency) account for more of the load in the recently expanded population than in populations that did not recently expand
  • more of the load in the non-expanded populations comes from a smaller number of variants that are at higher frequency in the population
  • the overall genetic load may not have been affected by differences in demography across populations
  • patterns of deleterious variation are, in fact, affected by demographic history differently than neutral variants
  • the average number of alleles per individual may be similar across populations
  • how those alleles are distributed into heterozygous and homozygous genotypes has been shown to differ across populations
  • 'the efficacy of selection' has not been reduced in non-African populations [37·]
  • this narrow definition of the 'efficacy of selection' only considers the efficacy of selection on a given variant, and does not account for the fact that the recent population expansion introduces many new deleterious mutations into the population
  • this increase in the number of deleterious mutations that enter the population as a result of the population expansion was considered a 'neutral force' by Do et al. [37·]
  • the distinction between 'reduced efficacy of selection' and increased importance of 'neutral forces' suggested by Do et al. [37·] is an unnecessary dichotomy