In human genetics, Haplogroup R1a1 (M17) is a [Y chromosome analysis? Y-chromosome haplogroup] that is spread across Eurasia.
It is common in Europe, Northern Central Asia and India. In Europe the highest frequencies are in Eastern Europe. Today it is found with its highest levels in Poland and Russia, where one out of two men has this haplogroup. Relatively high frequencies are also found in Northern Europe and is believed to have been spread across Europe by the Vikings, which accounts for the existence of it in, among other places, the British Isles. (1)
The first carriers of the R1a1 haplotype are believed to have been nomadic farmers in the steppes of east Europe about 10,000 years ago. Current theories point to them being the first speakers of the proto-Indo-European languages (the Kurgan culture) and the first ones to domesticate the horse.
Spread of haplogroup R1a. Image source
R1a1 is spread across whole of Europe, with the highest concentrations found in Eastern Europe. The two main directional components of the spread are consistent with a East to West migration as well as a radial spread from the Balkans. The latter is believed to be a trace of the re-population of Europe after the Last Glacial Maximum. (2)
The other two major genetic flow patters that can be seen from the R1a1 distribution are of the Slavic migrations from north eastern Europe to the Balkans as well as a distribution along the western coast of Europe and the British Isles which is believed to be connected to the Vikings.
In India initial studies observed a correlation between the Brahmin caste and the R1a haplogroup, which is consistent with a northern migration from Central Asia. Also, using PCA the gradients of the distribution of the haplogroup matched a spread that originated in the north (Cavalli-Sforza et al 2001). Other studies, with limited samples and without any diversity calculations confirmed this theory (Bamshad et al. 2001). The northern migration theory is also supported by the dating of the haplogroup which is consistent with archaeological evidence. (Wells et al 2003)
However, another study showed this lineage forms around 35-45% among all the castes in North Indian population (Namita Mukherjee et al. 2001) thus, making the association with Brahmin caste more vague. Yet another study, that found presence of R1a1 in South Indian tribals and Dravidian population groups questions the concept of its Aryan origin, (3) however this is refuted by the genetic context of India's northern neighbours.
Recently it has even shown a more diverse presence in Indian tribal and lower castes (the so-called untouchables and not part of the caste system) populations, suggesting that it is not necessarily always a signature of exclusive Indo-European origin.
As of June 2006, no statistically conclusive studies have been made in India, but what is clear is that the distribution is more complex than initially thought. The theory of northern migrations being the source of R1a1 in India is supported both by archaeological evidence and gradients of the genetic distribution as well as the dating of the haplogroup. The exclusive link to certain castes is however refuted by current the spread of the haplogroup. Another possible explanation for this is that the traditionally assumed link between migrants from north and castes is flawed.
It is clear however that more research is needed before a a consistent theory can be formulated.
Relationship to other haplogroups
R1a1 is a subgroup of [Haplogroup R (Y-DNA)? Haplogroup R] (M207).
It is related to [Haplogroup R1b (Y-DNA)? Haplogroup R1b] (M343) which is dominant in Western Europe, and more distantly related to [Haplogroup R2 (Y-DNA)? Haplogroup R2] (M124).
2. Pericic M, Lauc LB, Klaric IM, et. al. High-resolution phylogenetic analysis of southeastern Europe traces major episodes of paternal gene flow among Slavic populations. Mol Biol Evol. 2005 Oct;22(10):1964-75. PMID 15944443
3. Saha A, Sharma S, Bhat A, Pandit A, Bamezai R. Genetic affinity among five different population groups in India reflecting a Y-chromosome gene flow. J Hum Genet. 2005;50(1):49-51. PMID 15611834
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