Gene flow is the movement of alleles from one population to another through migration and reproduction. It matters because it changes how common different traits are in a population over generations. When beetles, birds, fish, pollen, or seeds move between habitats, they can carry gene variants with them.
This process helps explain why nearby populations of the same species often become genetically similar.
Key Facts
- Gene flow occurs when migrants reproduce in a new population and pass on their alleles.
- Allele frequency = number of copies of an allele / total copies of the gene in the population.
- If 20 of 100 alleles are blue, then pblue = 20/100 = 0.20.
- Gene flow tends to reduce genetic differences between populations over time.
- Gene flow can increase genetic variation within a population by adding new alleles.
- The allele frequency after migration can be estimated by p' = (1 - m)p + mq, where m is migration rate, p is the original population frequency, and q is the migrant frequency.
Vocabulary
- Gene flow
- Gene flow is the transfer of alleles between populations when individuals or gametes move and reproduce.
- Migration
- Migration is the movement of organisms, seeds, pollen, or gametes from one location or population to another.
- Allele
- An allele is a version of a gene that can produce variation in a trait.
- Allele frequency
- Allele frequency is the proportion of all gene copies in a population that are a particular allele.
- Genetic drift
- Genetic drift is a random change in allele frequencies, especially strong in small populations.
Common Mistakes to Avoid
- Treating migration alone as gene flow is wrong because migrants must reproduce for their alleles to enter the new population's gene pool.
- Assuming gene flow always creates new alleles is wrong because it usually moves existing alleles between populations, although those alleles may be new to the receiving population.
- Ignoring population size is wrong because the same number of migrants has a larger effect on a small population than on a large population.
- Thinking gene flow and natural selection always act in the same direction is wrong because gene flow can introduce alleles that selection removes or maintain variation that selection would otherwise reduce.
Practice Questions
- 1 Population A has 200 copies of a gene. If 50 copies are the red allele, what is the red allele frequency?
- 2 In Population B, the green allele frequency is p = 0.70. Migrants arrive with green allele frequency q = 0.20, and the migration rate is m = 0.10. Use p' = (1 - m)p + mq to find the new green allele frequency.
- 3 Two beetle populations live in different habitats. One habitat favors dark beetles, but light beetles frequently migrate in from a nearby population. Explain how gene flow could affect adaptation in the dark habitat.