Haplogroup K2a (M2308, Z4842) is a human Y-chromosome DNA haplogroup. K2a is a primary subclade of haplogroup K2 (M526), which in turn is a primary descendant of haplogroup K (M9). Its sole primary descendant is haplogroup K-M2313 (M2313, Z4858 S11799).
As of 2025, K-M2313 is known to have at least four primary subclades: Haplogroup NO1 (a.k.a. NO-M214), which has numerous members and the extremely rare subclades: K-Y28394, sometimes known as , K-FTC181, and K-MF106925.
Basal, undivergent K2a* (K-M2308*) has only been found in the remains of two Upper Paleolithic individuals, known as "Ust'-Ishim man and "Oase-1", who lived in Siberia and the Banat region of south-central Europe, respectively, about 37,000 to 45,000 years ago.
The current existing branches of K-M2313 are all downstream of K-F549. It diversified into subclades like NO-M214 include a majority of living males in East Asia, Southeast Asia, and Northern Eurasia. Rare subclades that do not belong to NO-M214 such as K-Y28299 has been found in individuals from India and Pakistan, K-F14963 has been found in individuals from the Toba Batak in Sumatra and the Mandar of Sulawesi. K-FTC181 and K-MF10925 has been found in individuals from Thailand and Vietnam respectively. These branches share a common ancestor with NO-M214 at K-F549.
According to geneticist Spencer Wells, haplogroup K probably originated in the Middle East or Central Asia, possibly in the vicinity of Iran or Pakistan. However, Karafet et al. (2014) proposed that "rapid diversification ... of K-M526", also known as K2, likely occurred in Southeast Asia and later expanded to mainland Asia, although they could not rule out that it might have arisen in Eurasia and later went extinct there, and that either of these scenarios are "equally parsimonius".
Before 2016, many authorities considered that the SNP M2308 was always found in conjunction with SNPs such as M2313 and M214. However, researchers such as G. David Poznik discovered examples of Y-DNA that had some, but not all, of the SNPs peculiar to NO (M214), but also lacked SNPs identifying other primary subclades of K2 (M526). Poznik et al. 2016 therefore identified K2a (M2308), K-M2313 and NO (M214) as "parent", "child" and "grandchild" clades respectively. While Poznik used the name "K2a1" for K-M2313, this has not been widely adopted, possibly because K2a1 has sometimes been used as an alternate name for other, less closely related haplogroups. Poznik et al. also found that K-Y28301, which has living members in India, is descended from K-M2313. The above findings by Poznik et al. were reiterated by the work of Moreno-Mayar et al. in 2018.
As of 2018, authorities like the International Society of Genetic Genealogy (ISOGG) have not integrated the discoveries of Poznik et al.
There is evidence of at least two additional primary branches within K-M2308 (Poznik: K2a) and/or K-M2313 (Poznik: K2a1).
After 2022, new clades downstream of K-F549 were detected, from scientific and personal samples of individuals across South Asia and Southeast Asia.
K2a K-M2308 (M2308, CTS11667)
? "NO1~" (CTS707/M2306) <br />
K2a* has been found only in the Paleolithic remains mentioned above:
K-M213(xNO-M214) was detected in samples from South and Southeast Asia.
Basal examples of haplogroup NO* have not been identified.
Subclades of haplogroup NO include a majority of living males in East Asia, Southeast Asia and Northern Eurasia.
K-Y28299(xY28301) has been found in individuals from India and Pakistan.
K-Y28301, a subclade of K-Y28299, has been found in living individuals with their origins in Andhra Pradesh and Arunachal Pradesh India.
K-F14963, another subclade of Y28394, has been found in individuals among the Toba Batak, Mandar, and other groups in Southeast Asia.
K-FTC181 and K-MF10925 has been found in individuals from Thailand and Vietnam.