thumb|500 Y-DNA phylogeny and haplogroup distribution. (a) Phylogenetic tree. 'kya' means 'thousand years ago'. (b) Geographical distributions of haplogroups are shown in color. (c) Geographical color legend.
In genetics, a Y-chromosome DNA haplogroup is a haplogroup defined by mutations in the non-recombining portions of DNA from the male-specific Y chromosome (called Y-DNA). Many people within a haplogroup share similar numbers of short tandem repeats (STRs) and types of mutations called single-nucleotide polymorphisms (SNPs).
The Y-chromosome accumulates roughly two 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 humans are descended patrilineally. Y-chromosomal Adam is estimated to have lived roughly 236,000 years ago in Africa. By examining other bottlenecks most Eurasian men (men from populations outside of Africa) are descended from a man who lived in Africa 69,000 years ago (Haplogroup CT). Other major bottlenecks occurred about 50,000 and 5,000 years ago and subsequently the ancestry of most Eurasian men can be traced back to four ancestors who lived 50,000 years ago, who were descendants of African (E-M168).
Naming convention
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 toward using the simpler shorthand nomenclature.
Phylogenetic structure
Phylogenetic tree of Y-DNA haplogroups
Major Y-DNA haplogroups
Haplogroups A and B
Haplogroup A is the NRY (non-recombining Y) macrohaplogroup from which all modern paternal haplogroups descend. It is sparsely distributed in Africa, being concentrated among Khoisan populations in the southwest and Nilotic populations toward the northeast in the Nile Valley. BT is a subclade of haplogroup A, more precisely of the A1b clade (A2-T in Cruciani et al. 2011), as follows: Haplogroup A Haplogroup A00 Haplogroup A0 (formerly also A1b) Haplogroup A1 (also A1a-T) Haplogroup A1a (M31) Haplogroup A1b (also A2-T; P108, V221) Haplogroup A1b1a1 (also A2; M14) Haplogroup A1b1b (also A3; M32) Haplogroup BT (M91, M42, M94, M139, M299) Haplogroup B (M60) Haplogroup CT
Haplogroup CT (P143)
The defining mutations separating CT (all haplogroups except for A and B) are M168 and M294. The site of origin is likely in Africa. Its age has been estimated at approximately 88,000 years old, and more recently at around 100,000 or 101,000 years old.
Haplogroup C (M130)