24.Allele, genotype and phenotype frequencies. Hardy-Weinberg equilibrium theory.
Covers how allele, genotype and phenotype frequencies are calculated, starting with the basic population genetics concepts of gene pool, natural selection and genetic drift. It then works through phenotype, genotype and allele frequency formulas with worked numerical examples, and explains the Hardy-Weinberg equation p² + 2pq + q² = 1. The note closes with the five assumptions for equilibrium and the forces that disrupt it, such as mutation, migration and selection.
Topic 24 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 407 words (3 min of reading), with 17 flashcards.
In this note
Allele, genotype and phenotype frequencies. Hardy-Weinberg equilibrium theory..
Population Genetics Overview
Phenotype Frequency
Genotype Frequency
Allele Frequency
Relationship Between Genotype & Allele Frequencies
Hardy–Weinberg Equilibrium
Population Genetics Overview
Population genetics studies how genes and alleles behave in populations and how their frequencies change over time.
Influencing factors include natural selection, mutation, gene flow, and genetic drift.
Additional influences: recombination, population subdivision, population structure.
Evolution at the population level starts when allele frequencies change across generations.
A population = individuals of the same species living together and interbreeding.
Evolution occurs at the population level, making it the smallest unit capable of evolving.
Key Concepts: allele
Gene pool: total set of all alleles at all loci in a population.
Natural selection: differences in survival/reproduction due to trait variation.
Genetic drift: random changes in allele frequencies, especially in small populations.
Phenotype Frequency
Proportion of individuals showing a particular observable trait.
Calculated: number with phenotype ÷ total population.
Example: 20 with albinism out of 100,000 → 0.0002.
Always between 0 and 1.
All phenotype frequencies for a trait must add up to 1.
Genotype Frequency
Proportion of individuals with a specific genotype.
Calculated: number with genotype ÷ total population.
Example: 4,000 MN genotype out of 10,000 → 0.4.
f(AA) + f(Aa) + f(aa) = 1.
If genotypes are distinguishable by phenotype (e.g., codominance), they can be determined directly.
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