Lecture 14: Hardy-Weinberg Equilibrium and Genotype Frequencies

Hardy-Weinberg Equation

Predicts allele and genotype frequencies at equilibrium.

Allele Frequency

Proportion of a specific allele in a population.

Genotype Frequency

Proportion of a specific genotype in a population.

Homozygous

Individual with two identical alleles for a trait.

Heterozygous

Individual with two different alleles for a trait.

p

Frequency of dominant allele in a population.

q

Frequency of recessive allele in a population.

p + q = 1

Sum of allele frequencies equals one.

p²

Frequency of homozygous dominant genotype (AA).

2pq

Frequency of heterozygous genotype (Aa).

q²

Frequency of homozygous recessive genotype (aa).

Genotype Frequency Formula

p² + 2pq + q² = 1.

Phenotypic Frequency

Proportion of individuals displaying a specific trait.

PTC Tasting

Trait influenced by a recessive allele.

Chi-Squared Test

Statistical test for comparing observed vs expected frequencies.

Random Mating

Mating without regard to phenotype or genotype.

Population Size

Influences allele frequency stability; must be large.

Migration

Movement of alleles between populations affecting frequencies.

Natural Selection

Differential survival affecting allele frequencies.

Mutation

New alleles introduced into a population.

Assumptions of Hardy-Weinberg

Conditions required for equilibrium predictions to hold.

Allele Count

Number of copies of an allele in a population.

Genotype Count

Number of individuals with a specific genotype.

f(S) Calculation

Frequency of S allele using genotype counts.

f(SS) Calculation

Frequency of SS homozygotes in a population.

Homozygous Frequency

Frequency of individuals with identical alleles.

Heterozygous Frequency

Frequency of individuals with different alleles.

Population Equilibrium

Stable allele frequencies over generations.

Allele Frequency Formula

Number of copies of allele/total alleles.

Genotype Frequency Example

f(SS) = #SS/N.

p² + 2pq + q²

Expanded form of Hardy-Weinberg equation.

Graphical Representation

Visualizes relationship between allele and genotype frequencies.

Equilibrium Conditions

Population must meet specific criteria to maintain stability.

H-W Predictions

Expected genotype frequencies based on allele frequencies.

Population Genetics

Study of genetic variation within populations.

Allele Frequency Change

Variation in allele proportions over generations.