Selective sweep of a novel
advantageous mutation:
Hitchhiking of
a linked neutral SNP
As previously shown, a new mutation (red SNP) in the sixth
chromosomal haplotype confers a strong selective
advantage and rapidly replaces the others in a selective "sweep".
Ordinarily this would eliminate the existing blue SNP. However, if
during the sweep, recombination occurs between
haplotypes ##5 & 6, the blue
SNP in #5 is transposed to a copy of #6,
creating a modified haplotype the combines the red & blue SNPs.
The selective sweep is driven by the
selective advantage of the red
SNP: the blue
SNP is carried along with the sweep by
linkage, irrespective of its neutral selective
advantage. This phenomenon is called "hitchhiking",
and makes determination of which of several linked SNPs
is actually subject to positive selection. For
example, although an inherited predisposition to a
disease may be mapped to an area of the short arm of a
chromosome in a particular family, because the entire
region is inherited as a linkage group, many SNP differences
between this region and homologous regions in other
unaffected families must be compared.
[NB: in such cases, the "candidate
gene" approach may be used to narrow the range of
SNPs to be examined to those that occur in genes
functionally related to the condition of interest].
Figure
modified after © 2013 by Sinauer; Text material ©
2021 by Steven M. Carr