admixture

Admixture in population genetics refers to the process by which an individual derives part of their ancestry from two or more previously separated populations. It typically results from historical interactions such as migration, colonization, trade, or lasting social barriers that break down isolation and allow interbreeding. When admixture occurs, the genome of descendants becomes a mosaic of ancestry from the source populations.

Admixed populations display segments of DNA that trace back to different ancestral sources. The pattern and length of these segments carry information about the timing and sources of admixture. Recent admixture tends to produce long genomic tracts, while older events yield shorter, more fragmented tracts due to recombination.

Scientists detect and quantify admixture using genome-wide data with methods such as model-based clustering (ADMIXTURE, STRUCTURE), principal components analysis, and ancestry-informative markers. Formal tests include f-statistics and D-statistics, and admixture graphs. Analyses of linkage disequilibrium and ancestry tracts contribute to timing estimates.

Examples include European, African, and Indigenous American ancestry in many contemporary Latin American populations, and widespread Neanderthal and Denisovan ancestry in non-African modern humans. Admixture affects allele frequencies and can influence disease risk, making ancestry a consideration in genetic studies.

Admixture also occurs in other species and is used in breeding to introduce desirable traits. Its study helps reconstruct demographic history and understand patterns of genetic diversity across populations.