The effect of differential reproductive success on allele frequencies within a gene pool
Some individuals reproduce more than others because their traits suit the environment better. Over generations, the alleles — gene variants — behind those traits become more common in the population.
Formula
Allele frequency = (number of copies of allele) ÷ (total number of all alleles at that locus)
Real World
The sickle-cell allele (HbS) remains at roughly 10–20% frequency in sub-Saharan African populations because carriers resist malaria — their differential survival keeps the allele common despite its harm in homozygotes.
Exam Focus
Explain the mechanism in order: selection pressure → phenotype advantage → more offspring → allele frequency rises over generations.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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