Evolutionary Genetics Cheat Sheet

The core ideas of Evolutionary Genetics distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/evolutionary-genetics/cheatsheet

Quick Reference

Natural Selection

The process by which organisms with heritable traits that confer a survival or reproductive advantage in a given environment tend to leave more offspring, causing those advantageous alleles to increase in frequency over generations.

Genetic Drift

Random fluctuations in allele frequencies from one generation to the next, caused by chance sampling of gametes. Drift is most powerful in small populations and can lead to the fixation or loss of alleles regardless of their fitness effects.

Mutation

A heritable change in the DNA sequence of an organism. Mutations are the ultimate source of all genetic variation and can range from single nucleotide substitutions to large-scale chromosomal rearrangements. Most mutations are neutral or deleterious, but occasionally a mutation confers a selective advantage.

Gene Flow

The transfer of genetic material from one population to another through migration and subsequent interbreeding. Gene flow tends to homogenize allele frequencies between populations and can introduce new genetic variation into a population.

Hardy-Weinberg Equilibrium

A mathematical model stating that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary forces (no mutation, no selection, no drift, no gene flow, and random mating). It serves as a null hypothesis against which real populations are compared.

Neutral Theory of Molecular Evolution

Proposed by Motoo Kimura in 1968, this theory holds that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutations rather than by positive natural selection. Neutral theory provides the foundation for the molecular clock concept.

Speciation

The evolutionary process by which populations diverge genetically and reproductively to become distinct species. Speciation can occur through geographic isolation (allopatric), ecological niche partitioning (sympatric), or partial barriers (parapatric).

Phylogenetics

The study of evolutionary relationships among organisms, typically represented as branching tree diagrams (phylogenetic trees). Modern phylogenetics uses DNA and protein sequence data along with computational algorithms to reconstruct the history of descent.

Fitness and Adaptation

Fitness is the relative reproductive success of a genotype in a given environment. Adaptation is the evolutionary process by which populations become better suited to their environment through the accumulation of beneficial genetic changes over successive generations.

Recombination and Linkage

Recombination is the exchange of genetic material between homologous chromosomes during meiosis, creating new combinations of alleles. Linkage refers to the tendency of genes located close together on the same chromosome to be inherited together. Recombination breaks down linkage over generations.

Key Terms at a Glance

Adaptation:A heritable trait that increases an organism's fitness in its environment, or the process by which such traits evolve.

Allele:One of two or more alternative forms of a gene at a particular locus on a chromosome.

Allopatric Speciation:Speciation that occurs when populations are geographically separated, preventing gene flow.

Balancing Selection:Selection that maintains multiple alleles in a population, such as through heterozygote advantage or frequency-dependent selection.

Bottleneck Effect:A drastic reduction in population size that reduces genetic variation and alters allele frequencies.

Coalescent Theory:A mathematical framework tracing alleles backward in time to their most recent common ancestor in a population.

Directional Selection:Natural selection that favors one extreme phenotype, shifting the population mean over time.

Effective Population Size:The size of an idealized population that experiences genetic drift at the same rate as the actual population.

Epistasis:A gene interaction in which the phenotypic effect of one gene depends on one or more other genes.

Fitness:The relative reproductive success of a genotype compared to others in a given environment.

Founder Effect:A form of genetic drift occurring when a small group establishes a new population with reduced genetic variation.

Gene Flow:The movement of alleles between populations through migration and interbreeding.

Genetic Drift:Random changes in allele frequencies across generations due to chance, most significant in small populations.

Genetic Load:The reduction in average fitness of a population due to the presence of suboptimal genotypes.

Hardy-Weinberg Equilibrium:A principle stating that allele frequencies remain constant in the absence of evolutionary forces.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.