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L. S. Emery and J. M. Akey
“Classical selective sweep” or “hard sweep”
“Soft sweep” from standing variation
“Soft sweep” with recurrent mutation
Selection on an epistatic variant
Selection on a microsatellite
Positive Selection Models
a
e
d
c
b
Fig. 9.1 Classical and alternative models of positive selection. Pink: causal variant under positive
selection. Cyan: hitchhiking variants. Blue: hitchhiking variants on a second haplotype background. Red: epistatic variant that affects the fitness of the selected variant. Left and right panels
denote patterns of variation before and after selection, respectively. (a) A new mutation arises and is
immediately advantageous. (b) An existing variant with multiple haplotype backgrounds is newly
advantageous due to a novel selective pressure. (c) During a selective sweep, the advantageous
variant arises again due to a mutation on a second haplotype background. (d) A new mutation
arises that is advantageous only in the presence of another variant due to epistatic interactions. (e)
A microsatellite locus is advantageous if the number of repeats is within a specific range; all other
repeat lengths have a lower fitness