Y-chromosomal haplogroup

In human genetics, a human Y-chromosome DNA haplogroup is a haplogroup defined by mutations in the non-recombining portions of DNA from the Y chromosome (called Y-DNA). Mutations that are shared by many people are called single-nucleotide polymorphisms (SNPs).

The human Y-chromosome accumulates roughly 2 mutations per generation. Y-DNA haplogroups represent major branches of the Y-chromosome phylogenetic tree that share hundreds or even thousands of mutations unique to each haplogroup.

The Y-chromosomal most recent common ancestor (Y-MRCA, informally known as Y-chromosomal Adam) is the most recent common ancestor (MRCA) from whom all currently living men are descended patrilineally. Y-chromosomal Adam is estimated to have lived roughly 236,000 years ago in Africa. By examining other bottlenecks all Eurasian men are descended from a man who lived 69,000 years ago. Another major bottleneck occurred about 5,000 years ago and subsequently most Eurasian men can trace their ancestry back to a dozen ancestors who lived 5,000 years ago.

Y-DNA haplogroups are defined by the presence of a series of Y-DNA SNP markers. Subclades are defined by a terminal SNP, the SNP furthest down in the Y-chromosome phylogenetic tree. The Y Chromosome Consortium (YCC) developed a system of naming major Y-DNA haplogroups with the capital letters A through T, with further subclades named using numbers and lower case letters (YCC longhand nomenclature). YCC shorthand nomenclature names Y-DNA haplogroups and their subclades with the first letter of the major Y-DNA haplogroup followed by a dash and the name of the defining terminal SNP.

Y-DNA haplogroup nomenclature is changing over time to accommodate the increasing number of SNPs being discovered and tested, and the resulting expansion of the Y-chromosome phylogenetic tree. This change in nomenclature has resulted in inconsistent nomenclature being used in different sources. This inconsistency, and increasingly cumbersome longhand nomenclature, has prompted a move towards using the simpler shorthand nomenclature. In September 2012, Family Tree DNA provided the following explanation of its changing Y-DNA haplogroup nomenclature to individual customers on their Y-DNA results pages (note that the haplogroup mentioned below relates to a specific individual):

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