Haldane's sieve and adaptation from the standing genetic variation.
We consider populations that adapt to a sudden environmental change by fixing alleles found at mutation-selection balance. In particular, we calculate probabilities of fixation for previously deleterious alleles, ignoring the input of new mutations. We find that "Haldane's sieve"--the bias against the establishment of recessive beneficial mutations--does not hold under these conditions. Instead probabilities of fixation are generally independent of dominance. We show that this result is robust to patterns of sex expression for both X-linked and autosomal loci. We further show that adaptive evolution is invariably slower at X-linked than autosomal loci when evolution begins from mutation-selection balance. This result differs from that obtained when adaptation uses new mutations, a finding that may have some bearing on recent attempts to distinguish between hitchhiking and background selection by contrasting the molecular population genetics of X-linked vs. autosomal loci. Last, we suggest a test to determine whether adaptation used new mutations or previously deleterious alleles from the standing genetic variation.
Orr
H A
HA
Department of Biology, University of Rochester, Rochester, NY 14627, USA. aorr@mail.rochester.edu
Betancourt
A J
AJ
D000220:Adaptation, Biological; D000483:Alleles; D000818:Animals; D005260:Female; D005808:Genes, Recessive; D008040:Genetic Linkage; D014644:Genetic Variation; D005828:Genetics, Population; D006801:Humans; D008297:Male; D008957:Models, Genetic; D015233:Models, Statistical; D009154:Mutation; D012737:Sex Factors; D013997:Time Factors; D014960:X Chromosome