Summary
A beneficial allele rising to fixation reduces nearby genetic variation through hitchhiking.
In depth
A strongly beneficial new mutation spreads rapidly, dragging linked neutral variants along (genetic hitchhiking), leaving a dip in diversity around it. Hard sweeps involve one origin and soft sweeps multiple.
Detecting sweeps highlights recent adaptation.
The signature of a sweep includes reduced diversity near the site, an excess of rare alleles, and long haplotypes with high frequency (extended haplotype homozygosity). Soft sweeps, from multiple origins or from standing variation, leave a weaker mark. Genomic scans such as iHS, Tajima's D and Fst outliers look for such regions.
Human examples include the lactase persistence allele in European and African pastoralists, the EPAS1 allele for high altitude in Tibetans (from Denisovan DNA), and skin pigmentation genes. In Drosophila and in the malaria parasite, sweeps mark drug resistance genes such as pfcrt.
Key idea: a sweep is selection in action at the DNA level, and linked sites are dragged along (hitchhiking).
Frequently asked questions
What is Selective Sweeps?
A beneficial allele rising to fixation reduces nearby genetic variation through hitchhiking.
Which area of biology covers Selective Sweeps, and how advanced is it?
Selective Sweeps is one of the 53 topics in Evolution. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Speciation Genomics, Evolution, Ancient DNA.
Can you give an example of Selective Sweeps?
Signals of sweeps are found around the lactase persistence gene in Europeans.
What should I learn before Selective Sweeps?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Selective Sweeps. Advanced topics assume the Intermediate vocabulary.
What topics are related to Selective Sweeps?
The closest topics to Selective Sweeps are Speciation Genomics, Evolution, Ancient DNA, Antibiotic Resistance Evolution. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Selective Sweeps?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Selective Sweeps. To practise the whole of Evolution, use the Evolution quiz.
How is Selective Sweeps different from Speciation Genomics?
Selective Sweeps: A beneficial allele rising to fixation reduces nearby genetic variation through hitchhiking. Speciation Genomics: Genome-wide analysis that identifies the loci and islands of divergence responsible for reproductive isolation. Read both side by side and note what each one explains.
How should I study Selective Sweeps step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Speciation Genomics and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.