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Haplogroup R (Y-DNA)
In human genetics, Haplogroup R is a Y-chromosome DNA haplogroup, a subgroup of haplogroup P, associated with the M207 mutation. It is believed to have occurred somewhere in Northwest Asia between 30,000 and 35,000 years ago. However, most of the rare forms of Haplogroup R chromosomes, as well as most cases of the closely related Haplogroup Q, are found among populations of Central Asia, South Asia, Australia, Siberia, Native Americans, Egypt and Cameroon.
One isolated clade (or clades) of Y chromosomes that appear to belong to Haplogroup R1* (M173-derived) is found at high frequency among the native populations of northern Cameroon in west-central Africa, which is believed to reflect a prehistoric back-migration of an ancient proto-Eurasian population into Africa; some researchers have reported having also detected Haplogroup K2 Y-chromosomes at a low frequency among some of these Cameroonian populations, which also suggests a Eurasian affinity. Some Y-chromosomes that appear to be closely related to the northern Cameroonian R1b1* are found at a substantial frequency among the modern population of Egypt. Many modern populations of northern Cameroon speak Chadic languages, which are classified as an ancient branch of the Afro-Asiatic superfamily of languages; the now extinct language of the Ancient Egyptians also belonged to the same superfamily.
Individuals whose Y-chromosomes possess all the mutations on internal nodes of the Y-DNA tree down to and including M207 (which defines Haplogroup R) but which display neither the M173 mutation that defines Haplogroup R1 nor the M124 mutation that defines Haplogroup R2 are categorised as belonging to group R*. Some instances of Haplogroup R* have been reported from samples of Australian aboriginal populations.
The subclades of haplogroup R with their defining mutation, according to the 2006 ISOGG tree:
R1a likely originated in the Eurasian Steppes, and may be associated with the Kurgan culture and Proto-Indo-European expansion. It is primarily found in Central and Western Asia, India, and the Slavic peoples of Eastern Europe, as well as among some populations of Mongolia and southern Siberia, where it might reflect Scythian influences of classical antiquity. Some researchers have objected to the association of Haplogroup R1a with Proto-Indo-Europeans, and believe instead that it reflects the traces of the ancient Scythian and Sarmatian domains, which they associate with the Indo-Iranian, Slavic, Satem Indo-European (Proto-Balto-Slavic-Indo-Iranian), Ugric, or even Turkic languages. One important observation that has been made about the frequently occurring subgroup R1a1 is that it appears to be very recently introduced in both the western and eastern extremes of its distribution: all the Haplogroup R1a1 Y-chromosomes found among the Czechs of Central Europe and the Khoton people of Mongolia coalesce to a common patrilineal ancestor who should have lived well within the bounds of the Neolithic, and possibly even within the bounds of historical time. This distribution is somewhat reminiscent of the widespread and frequently occurring subgroup of Haplogroup C3 that is believed to represent direct patrilineal descent from Genghis Khan. The R1a1 component of the Y-chromosome diversity among the Czechs suggests a rapid demographic expansion beginning about 60 to 80 generations ago, which would equate to about 1500 years ago (approx. 500 AD) to 2000 years ago (approx. 1 AD) with a generation time of 25 years. This means that the Y-chromosome distribution in the modern Czech population may be nothing but a magnified and perhaps somewhat modified version of the Y-chromosome distribution as it was in the region where the ancestors of the Czechs dwelt during the times of the Roman Empire.
Haplogroup R1a1 (M17) is spread across Eurasia. It is common in Europe, northern Central Asia, and South Asia. The first carriers of the R1a1 haplotype are believed to be have been peoples living about 10,000 years ago around Ukrainian LGM refuge area who after become nomadic proliferated on Eurasian steppes. Current theories point to them being speakers of the Proto-Indo-European language in the Kurgan scenario. In Europe, the highest frequencies are found among Eastern Europeans. Today it is found with its highest levels and diversity in Ukraine , where more than one out of two men has this haplogroup. It is found in high frequencies as well in Russia, Poland, and the Czech Republic, to name only a few, and relatively high frequencies are also found in Northern Europe and is believed to have been spread across Europe by the Vikings, which may account for the existence of it in, among other places, the British Isles.
Haplogroup R1b originated prior to or during the last glaciation, when it was concentrated in refugia in southern Europe and the Aegean. It is the most common haplogroup in Western Europe, but has been found at low frequency as far away as Iran and Korea. It is also found in North Africa where its frequency surpasses 10% in some parts of Algeria. In south-eastern England the frequency of R1b is about 70%; in parts of the rest of north and western England, Spain, Portugal, Wales and Ireland, it is as high as 90%; and in parts of north-western Ireland it reaches 98%. The R1b clade appears to have a much higher degree of internal diversity than R1a, which suggests that the M343 mutation that derives R1b from R1* may have occurred considerably earlier than the SRY1532 mutation that defines R1a.
R1b (previously called Hg1 and Eu18) is the most frequent Y-chromosome haplogroup in Europe. It is an offshoot of R1 (M173), characterised by the M343 marker. An overwhelming majority of members of R1b are classified as R1b1 (defined by the P25 marker), the remainder as R1b*. Its frequency is highest in Western Europe (and due to modern European emigration, in parts of the Americas). The majority of R1b-carriers of European descent belong to the subclade R1b1c (M269).
Haplogroup R2 (M124), found only in populations of South Asia, Central Asia, Iran, and the Caucasus. Haplogroup R2 is also found at a high frequency among certain groups of Roma (i.e., Gypsies), who are generally believed to have migrated into Europe and other regions from an ancient homeland in India.
The R2 subgroup is defined by marker M124. Unlike the other subgroups of R, R2 is confined to South Asia and nearby regions. The highest frequency is found in South Asia. It is also reported in lower frequencies in Caucasian and Central Asian populations.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Haplogroup_R_(Y-DNA)". A list of authors is available in Wikipedia.|