Haplogroup BT


Haplogroup BT M91, also known as Haplogroup A1b2, is a Y-chromosome haplogroup. BT is a subclade of haplogroup A1b and a sibling of the haplogroup A1b1.
Sufficient data is not always available to determine which, if any, member haplogroup a Y chromosome in BT belongs to. For instance, a survey of Y chromosomes in over 2000 men from different parts of Africa reported that 7.5% carried haplogroup BT, i.e. were members of haplogroup BT but not DE or K; such a sample might or might not include members of haplogroups B, C, or F, or some undiscovered branch of BT belonging to none of these.
I. Later Stone Age individuals excavated at Fingira Rock, Malawi, dated to around 6100 years ago, and at Mount Hora, Malawi, dated to around 8000 years ago, all belonged to Y haplogroup BT.

Phylogenetics

The ISOGG tree since 2014 has treated M91 as the defining mutation of BT.
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. They published a joint paper that created a single new tree that all agreed to use.