Genetic distance

Definition

A quantitative measure of genetic divergence between populations, species, or taxa, reflecting either the degree of allelic differentiation or the estimated time since divergence from a common ancestor. Genetic distance is typically calculated from molecular data (allozymes, microsatellites, mitochondrial or nuclear DNA sequences) and increases with reproductive isolation, geographic separation, and evolutionary time. In arthropod systematics, low genetic distances often indicate conspecific populations or recent divergence, while high distances support species-level or higher taxonomic separation.

Etymology

Example

Two allopatric populations of the butterfly Erebia medusa separated by Alpine glaciers show a genetic distance of 0.04 based on COI sequence divergence, suggesting Pleistocene divergence and warranting subspecies status; in contrast, sympatric cryptic species of the ant genus *Lasius* may exhibit distances exceeding 0.10, supporting their recognition as distinct biological species despite morphological similarity.

Synonyms

• genetic divergence
• molecular divergence

Related Terms

• genetic drift
• Gene flow
• population structure
• phylogeography
• Molecular clock
• cryptic species
• fixation index
• allele frequency
• reproductive isolation
• coalescent theory

Usage Notes

Genetic distance is model-dependent: raw sequence divergence (p-distance), Jukes-Cantor-corrected distances, and FST values measure different aspects of differentiation and are not directly comparable across studies. In insects and other arthropods with high mitochondrial mutation rates, distance thresholds for species delimitation vary widely among taxa and markers—COI 'barcode' gaps around 2-3% are heuristic guides, not universal rules. Specialists distinguish genetic distance (population-level) from phylogenetic distance (tree-based branch lengths).