--- title: "Selection Coefficients and Predicting Allele Frequency Change" description: "Giving each genotype a relative fitness turns selection into arithmetic: the frequency after one generation follows from the frequencies before and the fitnesses. Working the change out generation by " canonical: https://lightmysky.com/learn/science/selection-coefficients-and-predicting-allele-frequency-change-mt__JS2XJxOXV source: https://lightmysky.com/learn/science/selection-coefficients-and-predicting-allele-frequency-change-mt__JS2XJxOXV.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Selection Coefficients and Predicting Allele Frequency Change Giving each genotype a relative fitness turns selection into arithmetic: the frequency after one generation follows from the frequencies before and the fitnesses. Working the change out generation by generation shows how slowly a rare recessive allele is removed. Subject: Science · Area: Genetics & Evolution · Ages 18 to 19 Page: https://lightmysky.com/learn/science/selection-coefficients-and-predicting-allele-frequency-change-mt__JS2XJxOXV ## Ready when they can - Calculates allele frequency after one generation from genotype frequencies and fitnesses. - Explains why selection against a recessive allele slows as the allele becomes rare. - Distinguishes relative fitness from survival or family size taken alone. ## Lesson: Selection as bookkeeping Give every genotype a fitness number measured against the best one, and evolution turns into bookkeeping. Multiply each genotype frequency by its fitness and add them up for the mean fitness. Each allele's next frequency is its fitness weighted share divided by that mean. **Example.** A haploid population holds strain A at 0.5 with fitness 1.5, and strain a at 0.5 with fitness 0.5. Mean fitness is 0.75 plus 0.25, which is 1.0. The A share is 0.75, so its next frequency is 0.75 divided by 1.0, which is 0.75. A rare harmful recessive barely meets selection, since it shows only in homozygotes. At frequency 0.01 those appear once in ten thousand, while nearly every copy rides hidden inside healthy heterozygotes. Each generation removes a shrinking sliver, so progress stalls near zero. **Tip.** Fitness here is strictly relative, never health or years lived. Six offspring scores 0.75 where the best manages eight, whatever six means in absolute terms. Only the ranking steers allele frequencies. **Recap.** Weight frequencies by relative fitness, divide by the mean, and watch rare recessives hide. ## Practice 13 questions on this page, each with its working shown. ## Needs first - [The Hardy-Weinberg Principle and Allele Frequencies](https://lightmysky.com/learn/science/the-hardy-weinberg-principle-and-allele-frequencies-mt_eJjwZ2qVAE) - [Speciation and the Rate of Evolution](https://lightmysky.com/learn/science/speciation-and-the-rate-of-evolution-mt_OdcdfeRyo1) ## Opens up - [Cancer as Clonal Evolution: Drivers, Passengers and Selection in a Tissue](https://lightmysky.com/learn/science/cancer-as-clonal-evolution-drivers-passengers-and-selection-in-a-tissue-mt_3qIJZwD0m5) - [Sexual Selection, Mate Choice and Parental Investment](https://lightmysky.com/learn/science/sexual-selection-mate-choice-and-parental-investment-mt_6oTPGFw_p5) - [Genetic Drift and Effective Population Size](https://lightmysky.com/learn/science/genetic-drift-and-effective-population-size-mt_lbB1GbKv_t)