page_title: Haplogroup A-L1085
section_title: Cruciani 2011
hierarchical_section_title: Haplogroup A-L1085 / Phylogenetics / Phylogenetic history / Cruciani 2011
caption_attribution_description: English: Haplogroup A family tree
context_page_description: Haplogroup A-L1085, also known as haplogroup A0-T is a human Y-DNA haplogroup. It is part of the paternal lineage of almost all humans alive today. The SNP L1085 has played two roles in population genetics: firstly, most Y-DNA haplogroups have diverged from it and; secondly, it defines the undiverged basal clade A-L1085*.
  A0-T has two primary branches: A-V148 and haplogroup A-P305.
context_section_description: A major shift in understanding of the Haplogroup A tree came with the publication of (Cruciani 2011). Initial sequencing of the human y-chromosome suggested that first split in the Y-Chromosome family tree occurred with the M91 mutation that separated Haplogroup A from Haplogroup BT. However, it is now known that deepest split in the Y-chromosome tree is found between two previously reported subclades of Haplogroup A, rather than between Haplogroup A and Haplogroup BT. Subclades A1b and A1a-T now descend directly from the root of the tree. The rearrangement of the Y-chromosome family tree implies that lineages classified as Haplogroup A do not necessarily form a monophyletic clade. Haplogroup A therefore refers to a collection of lineages that do not possess the markers that define Haplogroup BT, though many lineages within haplogroup A are only very distantly related.
  The M91 and P97 mutations distinguish Haplogroup A from Haplogroup BT. Within Haplogroup A chromosomes, the M91 marker consists of a stretch of 8 T nucleobase units. In Haplogroup BT and chimpanzee chromosomes, this marker consists of 9 T nucleobase units. This pattern suggested that the 9T stretch of Haplogroup BT was the ancestral version and that Haplogroup A was formed by the deletion of one nucleobase.
  But according to Cruciani et al. 2011, the region surrounding the M91 marker is a mutational hotspot prone to recurrent mutations. It is therefore possible that the 8T stretch of Haplogroup A may be the ancestral state of M91 and the 9T of Haplogroup BT may be the derived state that arose by an insertion of 1T. This would explain why subclades A1b and A1a-T, the deepest branches of Haplogroup A, both possess the 8T stretch. Furthermore, Cruciani et al. 2011 determined that the P97 marker, which is also used to identify haplogroup A, possessed the ancestral state in haplogroup A but the derived state in Haplogroup BT.
caption: The revised y-chromosome family tree by Cruciani et al. 2011 compared with the family tree from Karafet et al. 2008. A1b is now known as A0 according to ISOGG.
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