Population, Quantitative and Evolutionary Genetics: every key term you need (+ practice quiz)
25 flashcard terms for Genetics Topic 8, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The complete set of alleles in a population, the level at which evolutionary change is measured rather than in any individual.
Allele frequency
The proportion of a locus's copies that are a given allele, the fundamental quantity that population genetics tracks over time.
Hardy-Weinberg equilibrium
The genotype proportions expected under random mating with no selection, mutation, migration or drift, and a large population.
Uses of the equilibrium model
It serves as a null expectation, so a significant departure signals that one of its assumptions is being violated and points to which force is acting.
Genetic drift
Random change in allele frequency from sampling in finite populations, strongest in small populations and able to fix alleles regardless of fitness.
Effective population size
The size of an ideal population that would drift at the observed rate. Unequal sex ratios and fluctuating numbers push it below the census count.
Founder effect
The distinctive allele frequencies of a population started by a few individuals, which explains locally common variants that are rare elsewhere.
Bottleneck
A sharp temporary reduction in numbers that removes variation. Diversity recovers far more slowly than population size does.
Gene flow
Movement of alleles between populations through migration, which reduces differences between them and can counteract local adaptation.
Natural selection
Differential reproduction linked to heritable variation, the only force that consistently produces adaptation to the environment.
Fitness and selection coefficient
Fitness is relative reproductive success and the selection coefficient measures the disadvantage of a genotype, together setting the speed of frequency change.
Directional selection
Favours one extreme, shifting the mean of the trait distribution and reducing variation at the selected locus.
Stabilizing selection
Favours intermediate values, narrowing the distribution while leaving the mean approximately unchanged.
Disruptive selection
Favours both extremes over the intermediate, which can produce a two-peaked distribution and begin to split a population.
Heterozygote advantage
Selection favouring the heterozygote, which maintains both alleles in the population and keeps a harmful recessive allele at a higher frequency than expected.
Frequency-dependent selection
An allele's fitness depends on how common it is, which can either preserve variation or drive cycles in frequency.
Mutation-selection balance
The equilibrium at which new harmful alleles appear as fast as selection removes them, explaining why rare deleterious alleles persist.
Inbreeding coefficient
The probability that an individual's two alleles at a locus are copies of the same ancestral allele, which raises homozygosity without changing allele frequencies.
Inbreeding depression
Reduced fitness in inbred lines caused by exposing recessive harmful alleles that heterozygosity had been masking.
Polygenic trait
A trait influenced by many loci of small effect, producing a continuous distribution rather than discrete classes.
Broad-sense heritability
The proportion of trait variation due to all genetic differences, an upper bound on how much of the variation has a genetic basis.
Narrow-sense heritability
The proportion due to additive effects only. It is the value that predicts response to selection, and it applies to a population rather than to an individual.
Breeder's equation
Predicts the response to selection as the narrow-sense heritability times the selection differential, which is why selecting hard on a low-heritability trait achieves little.
Gene by environment interaction
Genotypes ranked differently across environments, which means a heritability estimate from one setting does not transfer to another.
Molecular clock
The use of accumulated neutral substitutions as an approximate timer for divergence, calibrated against dated events and unreliable where rates differ.