Ingenetics, a subclade is a subgroup of a haplogroup.[1]
Although human mitochondrial DNA (mtDNA) and Y chromosome DNA (Y-DNA) haplogroups and subclades are named in a similar manner, their names belong to completely separate systems.[2]
mtDNA haplogroups are defined by the presence of a series of single-nucleotide polymorphism (SNP) markers in the hypervariable regions and the coding regionofmitochondrial DNA. They are named with the capital letters A through Z, with further subclades named using numbers and lower case letters.[2][3][4]
Y-DNA haplogroups are defined by the presence of a series of SNP markers on the Y chromosome. Subclades are defined by a terminal SNP, the SNP furthest down in the Y chromosome phylogenetic tree.[5]
The Y Chromosome Consortium (YCC) developed a system of naming major human 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.[6] 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.[7] This inconsistency, and increasingly cumbersome longhand nomenclature, has prompted a move towards using the simpler shorthand nomenclature.
A terminal SNP determines the terminal (final) subbranch on the Y-DNA Tree to which someone belongs.