Population Genetics & Hardy-Weinberg Vocabulary

Allele Frequency

The proportion of a specific allele in a population’s gene pool, expressed as a fraction or percentage.

Gene Pool

All alleles of all genes present in a reproducing population.

Microevolution

Small-scale change in allele frequencies within a population that does not produce a new species.

Macroevolution

Large-scale evolutionary change that results in speciation and reproductive isolation.

Speciation

The evolutionary process by which new, reproductively isolated species arise.

Hardy–Weinberg Principle

Mathematical model stating allele and genotype frequencies remain constant from generation to generation in the absence of evolutionary forces.

Hardy–Weinberg Equilibrium

The hypothetical, nonevolving state in which a population meets all Hardy-Weinberg conditions.

Genetic Equilibrium

Alternate term for Hardy-Weinberg equilibrium; allele frequencies do not change over time.

Null Hypothesis (Population Genetics)

Prediction that a population is in Hardy-Weinberg equilibrium; used as the baseline to detect evolution.

Natural Selection

Differential survival and reproduction of individuals with favorable heritable traits, altering allele frequencies.

Sexual Selection

Type of natural selection in which traits that improve mating success increase in frequency; involves nonrandom mating.

Nonrandom Mating

Mating pattern where certain phenotypes are preferred, violating Hardy-Weinberg’s random-mating assumption.

Mutation

Random change in DNA that creates new alleles and introduces genetic variation.

Genetic Drift

Random fluctuation of allele frequencies, especially strong in small populations or after population bottlenecks.

Gene Flow

Movement of alleles into or out of a population via migration, altering allele frequencies.

Random Mating

Condition in which all individuals have an equal chance to mate; required for Hardy-Weinberg equilibrium.

Dominant Allele

Allele that masks the expression of a recessive allele in a heterozygote.

Recessive Allele

Allele expressed only when homozygous; masked by a dominant allele in heterozygotes.

p (Hardy-Weinberg)

Symbol representing the frequency of the dominant allele in a population.

q (Hardy-Weinberg)

Symbol representing the frequency of the recessive allele in a population; p + q = 1.

Genotype Frequency

Proportion of a specific genotype (e.g., AA, Aa, aa) within a population.

Phenotype Frequency

Proportion of individuals displaying a particular trait in a population.

Homozygous

Having two identical alleles for a given gene (e.g., AA or aa).

Heterozygous

Having two different alleles for a given gene (e.g., Aa).

Adaptation

Inherited trait that increases an organism’s fitness in its environment.

Acclimation (Acquired Trait)

Non-genetic, learned or physiological adjustment that helps an organism cope