Haplogroup

A haplogroup is a genetic population group that shares a common ancestor at the level of a single genetic lineage, either the paternal Y chromosome or the maternal mitochondrial DNA. Haplogroups are defined by characteristic mutations, most commonly single nucleotide polymorphisms (SNPs), which mark branching points in the history of human lineages. In population genetics, haplogroups are used to trace ancient human migrations, geographic origins, and demographic events.

Y-chromosome haplogroups describe paternal lineages, since the Y chromosome is passed from father to son with limited recombination. They are designated by letter names and subclades (for example, R1b, which has many downstream branches). Mitochondrial DNA haplogroups describe maternal lineages, as mtDNA is inherited from mother to all offspring. Common mtDNA haplogroups include H, U, L, M, and N, with many subclades. The two systems reflect different histories and show distinct geographic patterns.

Nomenclature is maintained by phylogenetic trees, with ISOGG curating the Y-DNA haplogroup tree and databases like MITOMAP cataloging mtDNA haplogroups. Assignment relies on diagnostic SNPs obtained from genetic testing, ranging from targeted panels to full sequencing.

Applications include population genetics research, anthropological studies, forensic science, and genealogical testing. Haplogroups help infer ancestral connections and migratory routes, but they represent only a portion of ancestry and do not determine specific ethnicity or genealogical relationships between individuals. Limitations include genetic drift, population structure, sampling bias, and the fact that recombination largely limits haplogroup definitions to uniparental lineages.