Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving

Flashcards from Concept 23.2 of Pearson's Campbell Biology, Twelfth Edition.

Evolution

The changing of a species' genes over time, requiring genetic variation alongside other factors

Population

A group of individuals of the same species that live in the same area and interbreed

• If geographically isolated, genetic material is rarely exchanged

• Individuals typically only breed with members of their own population

Gene pool

All copies of every allele at every locus in all members of the population

Fixed locus

A locus that cannot change due to all individuals in a population being homozygous for the same allele; otherwise, individuals may be homozygous or heterozygous for two or more alleles

Genotype frequency

How frequent a specific genotype is in a population

• Calculated through the frequency of an individual genotype (like C^RC^R or C^RC^W) over the entire population combined

Allele frequency

How frequent a specific allele is in a measured population

• The total amount of alleles for diploid organisms is the amount of individuals times two

• Count two recessive or dominant alleles for each homozygous individual, and one of each allele for each heterozygote

• The frequency for each allele takes the number of each allele over the total amount of alleles, adding up to 1 when combining dominant (p) and recessive (q) alleles

p

The letter used to represent the allelic frequency of a dominant allele

q

The letter used to represent the allelic frequency of a recessive allele

Hardy-Weinberg Equation

An equation that describes the expected genetic makeup for a population not evolving at a particular locus, resulting in constant frequencies

• If the expected makeup differs from the population, evolution may be occurring — either through mutations, selective mating, natural selection, small population size, or gene flow

• Expressed as p² + 2pq + q² = 1

  • p² and q² represent the expected frequency of homozygous genotypes

  • 2pq represents the expected frequency of the heterozygous genotype

  • This is calculated separately from genotype frequency, only considering the allele frequency in an observed population