Overview
G2a* represents the paraphyletic basal layer of the G2a (P15) radiation, defined by the presence of P15 and closely linked markers such as U5, L31/S149 and L149 but by the absence of downstream diagnostic variants like L293 (G2a1), PF3147/M286 (G2a2a), L30/S126 (G2a2b) and others. In phylogenetic terms, G2a* stands for those early branches that diverged near the root of the G2a trunk and either left only a handful of descendants or remain insufficiently resolved by current sequencing. These basal lineages are important because they constrain the timing and geography of the initial G2a diversification before the better known Neolithic associated subclades arose.
Most men who carry G2a today belong to one of the major named subclades such as G2a1, G2a2 or G2a2b, but high coverage sequencing occasionally identifies P15 positive chromosomes that do not fit comfortably into these better defined branches. In a high resolution atlas, these lineages are grouped under G2a* to highlight that the G2a radiation began as a small set of Near Eastern and Caucasian groups during the Late Pleistocene and early Holocene, only some of which gave rise to large later expansions.
Geographic distribution
Modern G2a* lineages are extremely rare and have been reported at low frequency in the Near East, the Caucasus fringe and occasionally in southern Europe. These rare chromosomes often occur in regions that also display high diversity for G2a1, G2a2 and G2a2b, which suggests that the wider G2a trunk diversified in or near this broader Near Eastern highland corridor. Because G2a* is defined by the absence of downstream markers, its geographic signal is diffuse, but it helps anchor the deepest layers of G2a diversity in the Near East and surrounding regions rather than in Europe where Neolithic derived subclades dominate.
In Europe, individuals who initially appear as undifferentiated G2a* based on limited SNP panels often resolve into known G2a1 or G2a2 branches when tested on more complete Y sequencing platforms. Persistent basal G2a* cases are therefore most likely to be found in poorly sampled or mountainous regions of the Near East, the Caucasus and western Iran, where small refugial lineages could survive repeated demographic turnovers.
Ancient DNA
- Early Neolithic remains in Anatolia and the northern Fertile Crescent frequently carry G2a lineages that cannot be unambiguously assigned to later named branches, and some of these may represent now extinct or rare G2a* diversity.
- A subset of Pre Pottery Neolithic genomes from central Anatolia and northern Mesopotamia show basal G2a like profiles that phylogenetically sit near the root of the G2a trunk rather than within later G2a2b derived clusters.
- No ancient individual has yet been assigned to G2a* with full high coverage certainty, but several low coverage Neolithic and early Chalcolithic samples may fall into this category once more markers are recovered.
Phylogeny & subclades
Within the G2 framework, G2a* occupies the position of basal P15 derived lineages that sit upstream of G2a1 (L293), G2a2 (PF3147, including M286 and L91) and G2a2b (L30/S126 and P303) among others. It therefore represents the unresolved backbone at the base of the G2a tree. From this backbone emerge the major splits that structure the later G2a topology, including the L293 centered Caucasus branch, the PF3147/M286 centered Near Eastern and Mediterranean branches, and the L30/S126 and P303 centered Neolithic farmer lineages that dominate European G2a. In an atlas oriented phylogeny, explicitly including G2a* prevents the false impression that all G2a lineages neatly fall into a few large expansions and makes room for small, historically important but sparsely sampled branches.
- G2a* basal lineages with unresolved placement
- Near Eastern and Caucasus microclades lacking clear assignment to G2a1 or G2a2
- Potentially extinct early Holocene G2a branches visible only in ancient DNA
Notes & context
G2a* should be treated as a technical and historical category rather than as a coherent ethnically or geographically unified branch. It groups together the surviving remnants of early P15 bearing lineages that did not participate in the largest later expansions. For a mega haplogroup atlas, showing G2a* makes it easier to explain how the G2a trunk predates the massive Neolithic diffusion of agriculture into Europe and how several small Near Eastern refugial lineages co existed alongside the ancestors of well known G2a farmer clades.
References & external links