Population Genetics Exam 2 Study Guide

Key population genetics terms covering population structure, F-statistics, gene flow, natural selection, fitness, and mutation.

Metapopulation

A network of spatially separated subpopulations of the same species that are connected by occasional gene flow rather than mating panmictically.

Panmictic

A population condition characterized by completely random mating across the entire geographic range, lacking internal genetic or spatial structure.

Wright's Fixation Index ($F_{ST}$)

A metric of population structure that measures the degree of genetic differentiation and variation in allele frequencies among subpopulations within a metapopulation.

Wahlund Effect

The observed deficit of heterozygotes (and excess of homozygotes) in a combined sample from a structured population caused by allele frequency differences between isolated subpopulations.

$$F_{IS}$$

An F-statistic that measures inbreeding within subpopulations by assessing the reduction in observed heterozygosity compared to the expected heterozygosity of the subpopulation.

$$F_{IT}$$

An F-statistic measuring the total reduction in heterozygosity of an individual relative to the expected heterozygosity of the total metapopulation.

Gene Flow ($Nm$)

The genetic movement between populations, where $N$ is the effective population size and $m$ is the migration rate.

Absolute Fitness ($W$)

The total biological contribution of a genotype to the next generation, quantified as the raw number of surviving offspring produced.

Relative Fitness ($w$)

The survival and reproductive success of a genotype scaled relative to the most fit genotype in the population, typically set to $1.0$.

Selection Coefficient ($s$)

A quantitative measure of the reduction in relative fitness of a genotype compared to the favored genotype, calculated as $s = 1 - w$.

Directional Selection

A form of natural selection that consistently favors one phenotype or allele over alternatives, driving that allele toward higher frequency or fixation.

Stabilizing Selection

A form of natural selection that favors intermediate phenotypes over extreme phenotypes, maintaining population phenotypic averages.

Disruptive Selection

A form of natural selection that simultaneously favors individuals at both phenotypic extremes over individuals with intermediate phenotypes.

Negative Frequency-Dependent Selection

A form of balancing selection in which the relative fitness of a phenotype or genotype increases as it becomes rarer in the population.

Positive Frequency-Dependent Selection

A form of selection in which the relative fitness of a phenotype or genotype increases as its frequency in the population rises.

Adaptive Landscape (Fitness Landscape)

A conceptual representation depicting the relationship between population mean fitness and allele frequencies or genotypic combinations as peaks and valleys.

Balancing Selection

Natural selection that actively maintains multiple alleles or genetic polymorphism in a population, such as through heterozygote advantage or negative frequency dependence.

Nucleotide Transition

A point mutation interchanging purines ($A \rightleftharpoons G$) or pyrimidines ($C \rightleftharpoons T$), which is more likely to be neutral than a transversion.

Nucleotide Transversion

A point mutation that substitutes a purine for a pyrimidine or vice versa ($A \rightleftharpoons C$, $A \rightleftharpoons T$, $G \rightleftharpoons C$, or $G \rightleftharpoons T$).

Human Spontaneous Mutation Rate

The frequency of de novo single nucleotide changes occurring in humans, approximately equal to $1 \times 10^{-8}$ per nucleotide per generation.

Muller's Ratchet

The irreversible process in asexual populations whereby deleterious mutations progressively accumulate over time by drift, causing a continuous decline in population mean fitness.