Haplogroup BT M91, also known as Haplogroup A1b2 (and formerly as A4, BR and BCDEF), is a
Y-chromosome haplogroup. BT is a
subclade of haplogroup A1b (P108) and a sibling of the haplogroup A1b1 (L419/PF712).[2]
Distribution
Basal BT* has not been documented in any living individuals or ancient remains.
Later Stone Age individuals excavated at Fingira Rock,
Malawi, dated to around 6100 years ago (2/2 males), and at Mount Hora, Malawi, dated to around 8000 years ago (1/1 males), all belonged to Y haplogroup BT(xCT)[3] (i.e. they did not belong to haplogroup CT but may have belonged to haplogroup B).
No definite examples of BT(xCF,DE) – i.e. members of BT outside the only two known branches of CT, namely haplogroups
CF and
DE – have been identified. In some cases, because testing is undertaken only for geographically and historically likely haplogroups, the data required to identify a precise subclade has not been collected and/or recorded. For instance, research published in 2013, regarding a sample of more than 2,000 men from different parts of Africa, included 7.5% belonging to haplogroup BT(xDE,K).[4] These approximately 150 individuals may have included, for example: B*, unknown primary branches of haplogroups B, BT, CT or CF; haplogroup
C, and/or;
F(xK) (i.e. haplogroup F* plus its subclades G, H and IJ, but specifically excluding the broader
haplogroup K and its subclades, such as haplogroups K*, LT, K2b*, MS, NO, P, Q and R).
Phylogenetics
The
ISOGG tree since 2014 has treated M91 as the defining mutation of BT.[5]
Prior to 2002, there were in academic literature at least seven naming systems for the Y-Chromosome Phylogenetic tree. This led to considerable confusion. In 2002, the major research groups came together and formed the Y-Chromosome Consortium (YCC). They published a joint paper that created a single new tree that all agreed to use.
^ISOGG Haplogroup A (2012): "BT is shown on this tree, though it is not considered to be a part of Haplogroup A, in order to make it clear that, as a sibling clade of A1b1, BT and all other haplogroups are downstream of A1b. Listed 15 February 2012." (also note that the group labelled "A1b" in the image is the "A0" of
ISOGG (2012)).
^Van Oven M, Van Geystelen A, Kayser M, Decorte R, Larmuseau HD (2014). "Seeing the wood for the trees: a minimal reference phylogeny for the human Y chromosome". Human Mutation. 35 (2): 187–91.
doi:
10.1002/humu.22468.
PMID24166809.
S2CID23291764.
^ Haplogroup K2b (M1221/P331/PF5911) is also known as Haplogroup MPS.
^ Haplogroup K2e (K-M147) was previously known as "Haplogroup X" and "K2a" (but is a sibling subclade of the present K2a).
^K-M2313*, which as yet has no phylogenetic name, has been documented in two living individuals, who have ethnic ties to India and South East Asia. In addition, K-Y28299, which appears to be a primary branch of K-M2313, has been found in three living individuals from India. See: Poznik op. cit.;
YFull YTree v5.08, 2017, "K-M2335", and;
PhyloTree, 2017, "Details of the Y-SNP markers included in the minimal Y tree" (Access date of these pages: 9 December 2017)
^ Haplogroup K2b1 (P397/P399) is also known as Haplogroup MS, but has a broader and more complex internal structure.