Introgression

Definition

The long-term transfer of genetic material from one species into the gene pool of another through repeated backcrossing of interspecific hybrids with one parent species. Unlike intraspecific gene flow, introgression occurs across species boundaries and may require many hybrid generations before foreign alleles become established in the recipient population.

Etymology

Latin intro- (into) + gressus (step, going), reflecting the inward movement of genes across species boundaries

Example

In European honey bees (Apis mellifera), mitochondrial and nuclear markers from the African subspecies A. m. scutellata have introgressed into feral populations in the Americas following the expansion of "Africanized" hybrid swarms, creating a genetic mosaic that persists through continued backcrossing with local European-derived colonies.

Synonyms

• introgressive hybridization

Related Terms

• Gene flow
• hybridization
• backcrossing
• Horizontal gene transfer
• admixture
• reproductive isolation
• hybrid zone
• cytoplasmic introgression

Usage Notes

Distinguish from simple hybridization (any cross between species) and from gene flow within species. Introgression specifically requires the establishment of foreign alleles in a species' gene pool through repeated backcrossing, not merely the production of F1 hybrids. The process may be neutral, deleterious, or adaptive; adaptive introgression is increasingly documented in insects, as when resistance alleles cross species boundaries. In arthropod studies, mtDNA introgression is often detected before nuclear introgression due to its maternal inheritance and smaller effective population size. The term applies equally to natural, anthropogenic, and laboratory contexts.