Genetic Chaos

Friday, May 19, 2006

Where West Meets East: The Complex mtDNA Landscape of the Southwest and Central Asian Corridor

The southwestern and Central Asian corridor has played a pivotal role in the history of humankind, witnessing numerous waves of migration of different peoples at different times. To evaluate the effects of these population movements on the current genetic landscape of the Iranian plateau, the Indus Valley, and Central Asia, we have analyzed 910 mitochondrial DNAs (mtDNAs) from 23 populations of the region. This study has allowed a re-finement of the phylogenetic relationships of some lineages and the identification of new haplogroups in the southwestern and Central Asian mtDNA tree. Both lineage geographical distribution and spatial analysis of molecular variance showed that populations located west of the Indus Valley mainly harbor mtDNAs of western Eurasian origin, whereas those inhabiting the Indo-Gangetic region and Central Asia present substantial proportions of lineages that can be allocated to three different genetic components of western Eurasian, eastern Eurasian, and south Asian origin. In addition to the overall composite picture of lineage clusters of different origin, we observed a number of deep-rooting lineages, whose relative clustering and coalescent ages suggest an autochthonous origin in the southwestern Asian corridor during the Pleistocene. The comparison with Y-chromosome data revealed a highly complex genetic and demographic history of the region, which includes sexually asymmetrical mating patterns, founder effects, and female-specific traces of the East African slave trade.

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Investigation of the mitochondrial haplogroups M, BM, N, J, K and their frequencies in five regions in Iran

The frequencies of the Asian (M, BM) and European (N, J, K) mtDNA haplogroups in five major regions of Iran was investigated. Unexpectedly, the frequencies of the Asian haplogroups M and BM were low in Iran (2.34% for haplogroup M; 17.6% for haplogroup BM and 80.06% for haplogroup N). Almost identical frequencies for haplogroups J and K were found in the present study (10.81% and 10.14% for haplogroups J and K, respectively). On the other hand, the frequencies of haplogroups M and BM in Eastern regions were more than their frequencies in Western regions of the country. In contrast, the frequencies of haplogroups J and K in Western regions were more than their frequencies in Eastern regions of Iran. As a result, this study gives evidence for similarity between Iranian population ethnic groups and people from Northwest Asia and Southeast Europe. Our data suggest that Iranian tribes probably played a remarkable role in the formation of these ethnic groups. It gives the indication that the haplogroup J may be older than 6000-10000 years, and probably developed in Iran, and then expanded to different regions in Europe and Northwest Asia. On the other hand, it seems that the super-haplogroup M has developed after the inhabitants of Iran moved to Eastern Asia or this group migrated from Southern Iran/North of Arabian halve O to Pakistan and then to Asia.

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Concomitant Replacement of Language and mtDNA in South Caspian Populations of Iran

The Gilaki and Mazandarani occupy the South Caspian region of Iran and speak languages belonging to the North-Western branch of Iranian languages. It has been suggested that their ancestors came from the Caucasus region, perhaps displacing an earlier group in the South Caspian. Linguistic evidence supports this scenario, in that the Gilaki and Mazandarani languages (but not other Iranian languages) share certain typological features with Caucasian languages. We analyzed patterns of mtDNA and Y chromosome variation in the Gilaki and Mazandarani. Based on mtDNA HV1 sequences, the Gilaki and Mazandarani most closely resemble their geographic and linguistic neighbors, namely other Iranian groups. However, their Y chromosome types most closely resemble those found in groups from the South Caucasus. A scenario that explains these differences is a south Caucasian origin for the ancestors of the Gilaki and Mazandarani, followed by introgression of women (but not men) from local Iranian groups, possibly because of patrilocality. Given that both mtDNA and language are maternally transmitted, the incorporation of local Iranian women would have resulted in the concomitant replacement of the ancestral Caucasian language and mtDNA types of the Gilaki and Mazandarani with their current Iranian language and mtDNA types. Concomitant replacement of language and mtDNA may be a more general phenomenon than previously recognized.

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