| Haplogroup G2a1 | |
| Possible time of origin | perhaps 3,000 years BP |
| Possible place of origin | perhaps southern Caucasus Mtns. |
| Ancestor | Haplogroup G2a (P15) |
| Descendants | G2a1a |
|---|---|
| Defining mutations | P16 (G2a1), P18 (G2a1a) |
In human genetics, Haplogroup G2a1 (P16) is a Y-chromosome haplogroup. It is a branch of haplogroup G (Y-DNA) (M201), and more specifically of haplogroup G2 (P287) and most specifically of haplogroup G2a (P15). Haplogroup G2a1 has an extremely low frequency in almost all populations except in the area of the Caucasus Mountains.
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Almost all G2a1 persons have a value of 10 at short tandem repeat (STR) marker DYS392. They also typically have higher values for DYS385b, such as 16, 17 or 18, than seen in most G persons. Almost all G2a1 persons have a value of 15 or more at DYS385a, a finding which can be helpful in distinguishing G2a1 persons from non-G persons with similar marker values. In addition, the G2a1 persons tested were found to have a value of 9 at marker DYS505. This is several values below what is found in G subgroups, and is potentially the basis of additional subgrouping.
Under usual circumstances G2a1 persons would also have the distinctive mutation at SNP P16 that characterizes G2a1. The reliability of P16 in identifying everyone who should be P16+ has been questioned.[1] Because there are two strands involved, P16 results can be reported as P16.1 and P16.2, and persons may have varying results for components of the SNP. The P designation in P16 indicates it was identified at the University of Arizona, and P16's existence was first reported in 2000.[2] These are the specifications listed for P16: located on the Y chromosome at 19434578; 19128376.....forward primer is aggctccatctgtagcacac.....reverse primer is taaccttatagaccaaccccg...the mutation is a change from A to T.[3]
In August 2010 G2a1 persons tested for the DYS505 STR marker. They were found to have a value of 9, which is a multistep mutation from the usual 11 or 12 seen in all other tested haplogroup G persons. This marker value oddity may become more important than the SNP tests in grouping G2a1 persons.
While the G2a1 mutation has not been dated in a scholarly publication, the number of mutations seen in G2a1 67-marker samples suggests probably P16 arose not much more than 3,000 years ago and that the Caucasus G2a1 cluster had shown splitting of specific clusters from the main group, as well as splitting within nonclustering men, in the range of 2,000 or more years ago probably related to geographical migrations.
The presence of the SNP P18 mutation characterizes G2a1's only subgroup, G2a1a. The reliability of P18 in identifying everyone in the G2a1a category has been questioned.[1] Because individual strands are examined, P18 can be classified as P18.1, P18.2 and P18.3, and persons may have varying results for three components. The P designation indicates it was identified at the University of Arizona, and its existence was first reported in 2002.[4] The technical specifications for P18 are that it is: located on the Y chromosome at 25751219; 25029753; 23396005....forward primer is tggatctgattcacaggtag....reverse primer is ccaacaatatgtcacaatctc.....the mutation is a change from C to T.[3]
Due to the unreliability of the SNP testing for this haplogroup, it can be difficult to validate whether identificable clusters of men belong to G2a1 or instead to G2a1a. The most common cluster based on STR marker values of G2a1 men who report ancestry in the Caucasus Mountains region has the value of 9 at STR marker DYS391 and 19,21 at marker YCA. Significant other smaller G2a1 Caucasus clusters with 10 or 11 at DYS391 also exist.
The Ashkenazi Jewish G2a1 men with northeastern European origins almost all have YCA values of 21,21 and a DYS19 value of 16. More variation in values is seen in the Caucasus samples than the Ashkenazi samples, suggesting an older common ancestor in the Caucasus than among the Jews.
Other G2a1 men reporting eastern European ancestry form a cluster with YCA values of 19,21 without the other distinctive values seen in the other two clusters.
About half of the available G2a1/G2a1a samples do not reliably belong to any of these three clusters. In addition, the STR markers mentioned are prone to further mutations and are not as reliable as SNPs in identifying all the persons who share a common male ancestor.
There exist several genetic clusters of men whose STR marker values share many similarities with G2a1 men including DYS392=10. The men in these clusters were found G2a, but negative for P16. It is unclear whether their ancestors have lost the P16 mutation or whether they share an ancestor with G2a1 men about the time the P16 mutation occurred. While these other persons comprise the closest matches to G2a1 persons based on number of STR mutations, the number of marker value differences seen in comparisons is substantial.
G2a1 and its one subgroup represent the majority of haplogroup G samples in some parts of the Caucasus Mountains area. G2a1 is found only in tiny numbers elsewhere.
A recent article by Balanovsky et al.[5] provided the first detailed testing of P16 and P18 in this region.
Almost all P16 samples also had the P18 mutation. The highest percentage of P18 was found among Ossetians of Russia's Republic of North Ossetia-Alania, representing 32% of all samples there. Among Abkhazians of Abkhazia, P18 was 16% of total samples, and it was 8% of Circassians (Adyghe) in Russia's Republic of Karachay-Cherkess. Elsewhere in the Caucasus, P16 and P18 were negligible or represented a small percentage. The southeastern Caucasus area was not sampled.
There are isolated samples of G2a1 men with reported ancestry in Georgia, Turkey, Bulgaria, western Russia, Libya, and England with similarities to those of a North Ossetian cluster based on STR marker values. Likewise closely related to a Jewish cluster based on STR marker values is an anonymous sample in the SMGF database from Kashgar, China,[6] as well as isolated samples from Lebanon, Cyprus, Armenia and the Austrian Tyrol. The eastern European cluster includes an anonymous sample in the SMGF database [6] from Kyrgyzstan.
There are also isolated samples that do not belong to any cluster from the major countries of central, eastern and southern Europe, from Morocco, the northern Middle East, the Caucasus region and Iran.[7] The sample from Iran (Tehran) represents only 1 of the 444 Iranian samples of all types in the YHRD database. Possibly of significance—unlike some other G subgroups—G2a1 samples from southern Asia do not seem to exist.[8] In contrast, among the Romani of Hungary many of the available haplogroup G samples have STR marker features typical of G2a1.[9]
The exceptionally high level of G2a1 in the North Ossetians has attracted attention and speculation. Since the Ossetians make claim to descent from the Alans, a group of Sarmatians, it was thought that the Alans or their predessor residents of the area north of the Caucasus, the Scythians, must also have been high in Haplogroup G. In addition, a possible connection to the Alans was of interest because certain areas of Europe have a distribution of haplogroup G incorresponding to those to which large numbers of Alans and other Sarmatians migrated.
The type of haplogroup G in these European areas, however, is not G2a1 which is rare in Europe. Also rare in Europe is the type of G (G2a3b1) common among the Kabardinians of the northwestern Caucasus adjacent to the Ossetians.
If the Ossetian G2a1 originated in the major groups north of the Caucasus sometime during an approximate 2,000-year period, it would have been sequentially either from the Scythians, the Alans (and other Saramatians) or the Huns. All three groups were described north of the Caucasus in different time periods as they migrated from the east. Examination of ancient DNA from Scythian skeletons from the steppes to the east of the Caucasus has found only haplogroup R1a.[10][11] The Sarmatians subsumed the Scythians. Then many of the Sarmatians migrated westward into Europe. Then the Huns occupied the area north of the Caucasus prior to their own migration farther westward involving large numbers of men. Finally, the Mongols in their migration into the area north of the Caucasus forced what are thought to be the ancestors of modern Ossetians southward down to the edge of the mountains.
These three groups that occupied the area to the north of the Caucasus had language and cultural similarities. But they were also considered just confederations of various tribes. Sarmatians in particular were known readily to accept other groups into their numbers.[12] Because all three groups were also nomadic and often relocating in mass migrations, it is conceivable they vacated the last residence leaving little genetic trace of their occupation within the next occupants.
Only the Scythians were mentioned in historical records as having a connection south of the Caucasus where significant concentrations of haplogroup G exist. Greek historian Diodorus Siculus related that the Scythians had carried Medes to the River Don north of the Caucasus presumably from today's northwestern Iran, this event giving rise to their name Sauromatians.[13] Scythians had occupied Media 653-625 BCE. Pliny also suggested Sarmatians descended from Medes.[14] But historians have difficulty explaining how the Sarmatians instead seemed to come from central Asia off to the east in their occupation of Scythian lands around the 5th century BCE. The Median lands were primarily in northwestern Iran, and the G samples found there do not resemble the types or patterns seen in the Caucasus.
In the Nasidze study of Y-DNA in various Caucasus groups,[15] he concluded that the groups north of the Caucausus are closer genetically to each other than to persons south of the Caucasus. But he used only brief STR marker samples, and more samples and more detailed ones are now available.[16] These latter samples indicate the G2a1 found in the North Ossetians is most frequently found also south of the Caucasus and rarely elsewhere.
If a concentration of G2a1 points to the location of its origin, the north and south Caucasus region would be the likely location of origin. However, the first ancestors who were G2a1 could have been small in number, and a relocation from elsewhere is possible. The most important factor in determining G2a1 origins is knowing where the North Ossetians came from. Because of the confederation nature of the Alans, it is possible the Ossetian ancestors were part of those Alans who did not participate in the Great Migration. But it also seems plausible that the pre-Alan ancestors of the North Ossetians arrived there from south of the Caucasus where G is found in significant numbers and with the diversity seen in a longtime presence. The G in the area to the north of the Caucasus lacks both features.
Joseph Stalin, from genetic testing of his grandson (his son Vasily's son; Alexander Burdonsky) belongs to haplogroup G2a1a.[17] The STR marker value combinations for him are typical of those seen primarily in the Caucasus region.[18]