Gene flow can wash out local adaptation
- The idea
- Predict
- See it
- Why
- Check
The idea
“Gene flow just brings in new alleles, so it gives a population more variation for selection to use.”
New alleles sound like raw material for evolution, so gene flow sounds like a gift. The migrants bring their home allele frequencies too, and those may fit a different place.
The short version
The mistake: Gene flow just brings in new alleles, so it gives a population more variation for selection to use.
What's actually true: Gene flow can bring in new alleles, but it also makes populations more alike and can undo local adaptation.
- Gene flow is the movement of alleles between populations, by migrants or pollen. Arrivals carry their home population's alleles.
- Selection removes some poorly suited alleles each generation, and gene flow keeps bringing them back. Enough gene flow can swamp a local adaptation.
- Over time, gene flow makes connected populations more alike. Because it shifts allele frequencies, the Hardy-Weinberg model assumes there is none.
On the exam: Ask what the migrants carry. Gene flow pulls a population toward the source's allele frequencies.