Population Genetics: Selection & Evolutionary Genetics

This set of vocabulary flashcards covers essential terms and measures in population genetics, including types of fitness, selection coefficients, and different modes of natural selection.

Biological evolution

Genetic change in a group of organisms.

Anagenesis

Evolution taking place in a single group (a lineage) with the passage of time.

Cladogenesis

The splitting of one lineage into two, leading to the emergence of new species.

Fitness ($\omega$)

An organism’s success in passing its genes to the next generation, defined by its ability to survive, find mates, and reproduce in a given environment.

Absolute Fitness ($W$)

The per-capita growth rate of a genotype, calculated as the probability of survival multiplied by the average number of offspring.

Relative Fitness ($\omega$)

The absolute fitness of a genotype divided by the highest absolute fitness in the population, often standardized to the most successful genotype.

Inclusive Fitness

A measurement that includes an individual's own offspring and the impact they have on the reproduction of relatives who share their genes.

Selection coefficient ($s$)

A measure of the intensity of selection against a genotype, defined by the relative reduction in fitness; calculated as $s = 1 - W$.

Directional selection

A mode of natural selection where a single, extreme phenotype is favored, causing the allele frequency to shift over time in that direction and often leading to fixation.

Stabilizing selection

A type of selection where intermediate phenotypes are favored and extremes are removed, resulting in decreased variation.

Disruptive selection

A form of natural selection where both extreme phenotypes are favored over the mean, which may lead to population divergence and a bimodal distribution.

Overdominance

Also known as heterozygote advantage; a condition where the heterozygote has higher fitness than either homozygote, maintaining genetic variation in a stable equilibrium.

Underdominance

A condition where the heterozygote has a lower fitness than either homozygote, leading to an unstable equilibrium.

Genetic drift

An evolutionary force consisting of random changes in allele frequencies that can lead to the fixation of one allele, particularly in small populations.

Theodosius Dobzhansky

The biologist who stated, "Nothing in biology makes sense except in the light of evolution."

Balancing selection

The collective name for forces such as mutation, overdominance, and changing environments that explain why genetic variation persists.