Selective sweep of a novel advantageous mutation
The left-hand panel shows patterns of eight SNPs
in six distinct haplotypes among eight (haploid)
individuals: ##1 & 2, and 4 & 5 are identical.
Note that #3 differs from ##1 & 2, and #8 from #7, by
single new SNPs.
A novel SNP indicated by the red star arises by a new mutation in a single individual, #6. The linked SNPs to the left & right are shared with the haplotype in ##4 & 5, which indicates common ancestry.
If the novel SNP confers a major adaptive advantage, strong positive selection will take it to fixation in a few generations. Genetically linked SNPs on either side will also become fixed, even though they are selectively neutral, with no selective advantage in themselves. Natural Selection therefore "sweeps" all genetic variation out of the chromosome region. Such a sweep occurs only in the absence of genetic recombination, and is therefore expected to be limited to a relatively small region.
A novel SNP indicated by the red star arises by a new mutation in a single individual, #6. The linked SNPs to the left & right are shared with the haplotype in ##4 & 5, which indicates common ancestry.
If the novel SNP confers a major adaptive advantage, strong positive selection will take it to fixation in a few generations. Genetically linked SNPs on either side will also become fixed, even though they are selectively neutral, with no selective advantage in themselves. Natural Selection therefore "sweeps" all genetic variation out of the chromosome region. Such a sweep occurs only in the absence of genetic recombination, and is therefore expected to be limited to a relatively small region.
The utility of neutral
markers to detect genetically-linked
disease SNPs was
discussed in Biol2250.
Figures © 2013 by Sinauer; Text material © 2021 by Steven M. Carr