Overview
J2a-M68 is one of the oldest and most geographically distinctive branches of the J2a clade, with a distribution that strongly emphasizes South Asia and adjoining regions. Phylogenetically it descends from the Z6057 cluster under L26 and represents an early offshoot that diverged before the main Mediterranean and Near Eastern centered J2a expansions. Its deep time depth suggests that it formed among late Pleistocene or early Holocene populations living between the Iranian plateau and northwestern parts of the Indian subcontinent.
The present day concentration of M68 in South Asia indicates that a substantial portion of its downstream diversification occurred within the subcontinent, likely in association with early Holocene hunter gatherer and early agricultural populations. Archaeogenetic and comparative frequency data support a scenario in which M68 was involved in the formation of regional Neolithic and later Chalcolithic societies in northwest India and Pakistan, while retaining upstream connections to the wider West Asian J2a pool. Unlike some other J2a lineages that experienced large scale Mediterranean or Anatolian centered expansions, M68 appears to have followed a more easterly, South Asia linked trajectory.
Geographic distribution
Most frequent in northwest India and Pakistan, with additional presence in other parts of the Indian subcontinent and low to moderate frequencies in Iran, Afghanistan and Central Asia. Occasional occurrences in the Near East likely represent back migrations or recent movements.
Ancient DNA
- Indirect evidence from South Asian Chalcolithic and early historic genetic profiles indicates the presence of J2a lineages compatible with ancestral M68.
- Comparative analyses of modern populations show continuity between northwestern Indian and Pakistani M68 carriers and older West Asian J2a backgrounds.
- Genome wide studies of Neolithic and later South Asian population structure support an early introduction of West Eurasian male lineages including J2a into the subcontinent.
- Ancient DNA from Iran and the Iranian plateau reveals J2a diversity that can plausibly include upstream relatives of M68.
- Patterns of coalescent ages for M68 and its upstream nodes are consistent with Holocene population growth in South Asia.
Phylogeny & subclades
M68 is an early branch under J2a-Z6057 and forms a South Asia linked cluster that is phylogenetically separated from the more western Mediterranean and Near Eastern J2a expansions. Its internal structure shows several subbranches that appear to have diversified primarily within South Asia.
- J2a-M68*
- South Asian downstream clusters
- Iranian plateau related microbranches
Notes & context
J2a-M68 is particularly important for understanding the eastern range of J2a expansions and the contribution of West Eurasian paternal lineages to the early genetic history of South Asia.
References & external links