Mutation, Gene Flow and the Balance That Holds Variation
Mutation makes new alleles slowly and migration moves existing ones between populations quickly, while selection and drift remove them. What is observed is the balance of those inputs and outputs rather than any of them alone.
What a learner can do afterwards
- Explains why a harmful recessive allele persists at low frequency instead of disappearing.
- Predicts what steady migration does to the difference between two populations.
- Ranks mutation and migration by how fast each changes a frequency.
1 · Read
With no force acting, allele and genotype frequencies freeze at p squared plus 2pq plus q squared. That Hardy Weinberg stillness is the baseline. Any lasting shift means some force is at work: mutation, migration, selection, or drift.
Mutation is the only force that creates brand new alleles, but it trickles drop by drop and needs thousands of generations to matter alone. Migration ferries whole sets of alleles across borders each generation, so even one migrant per generation can blend two groups. For short term change, migration dominates; for novelty, mutation rules.
A harmful recessive lingers because most copies hide in healthy heterozygotes, out of selection's reach. Only the rare homozygote pays the cost, so removal crawls. Meanwhile steady migration pulls two groups toward each other a little every generation until their gap nearly closes.
To estimate q, take the square root of the recessive homozygote frequency. If 4 in 100 show the recessive trait, q is the square root of 0.04, which is 0.2. What you observe is always the balance of inputs and outputs, never one force alone.
New alleles trickle in, migrants blend groups fast, and hidden recessives linger.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.