Genetic Chaos

Friday, December 09, 2005

Patterns of male-specific inter-population divergence in Europe, West Asia and North Africa

We typed 1801 males from 55 locations for the Y-specific binary markers YAP, DYZ3, SRY10831 and the (CA)n microsatellites YCAII and DYS413. Phylogenetic relationships of chromosomes with the same binary haplotype were condensed in seven large one-step networks, which accounted for 95% of all chromosomes. Their coalescence ages were estimated based on microsatellite diversity. The three largest and oldest networks undergo sharp frequency changes in three areas. The more recent network 3.1A clearly discriminates between Western and Eastern European populations. Pairwise Fst showed an overall increment with increasing geographic distance but with a slope greatly reduced when compared to previous reports. By sectioning the entire data set according to geographic and linguistic criteria, we found higher Fst-on-distance slopes within Europe than in West Asia or across the two continents.

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Phylogeographic Analysis of Haplogroup E3b (E-M215) Y Chromosomes Reveals Multiple Migratory Events Within and Out Of Africa

We explored the phylogeography of human Y-chromosomal haplogroup E3b by analyzing 3,401 individuals from five continents. Our data refine the phylogeny of the entire haplogroup, which appears as a collection of lineages with very different evolutionary histories, and reveal signatures of several distinct processes of migrations and/or recurrent gene flow that occurred in Africa and western Eurasia over the past 25,000 years. In Europe, the overall frequency pattern of haplogroup E-M78 does not support the hypothesis of a uniform spread of people from a single parental Near Eastern population. The distribution of E-M81 chromosomes in Africa closely matches the present area of distribution of Berber-speaking populations on the continent, suggesting a close haplogroup–ethnic group parallelism. E-M34 chromosomes were more likely introduced in Ethiopia from the Near East. In conclusion, the present study shows that earlier work based on fewer Y-chromosome markers led to rather simple historical interpretations and highlights the fact that many population-genetic analyses are not robust to a poorly resolved phylogeny.

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YAP, signature of an African–Middle Eastern migration into northern India

YAP, an Alu insertion polymorphism found on human Y-chromosome is present in two lineages worldwide, corresponding to M145/M203/SRY4064 (haplogroup E) and M145/M203/M174 (haplogroup D) polymorphisms respectively. First lineage belonging to haplogroup D is specific to Japan and other Southeast Asian populations, while haplogroup E is confined to Sub-Saharan African, Middle Eastern and Southern European populations. In the present study, 1021 Y-chromosomes belonging to nine different populations of North India were analysed for YAP insertion and four other single nucleotide polymorphisms (SNPs) to delineate the two lineages. Out of nine populations only one, i.e. Shiya Muslims revealed presence of YAP element at a frequency of 11%. Further analysis based on four additional SNPs revealed that all the YAP+ve samples could be categorized under African/Middle East-specific haplogroup E lineage. Interestingly, Sunni Muslims who historically have the same origin, i.e. from the Middle east showed a complete lack of YAP+ve lineage similar to other castes. We hypothesize that unlike Sunnis, Shiya Muslims due to their lesser number and less admixture with other caste groups of India, still carry the ancestral YAP+ve lineage, which in all probabilities is one of the founder haplogroups. All Middle Eastern populations show the presence of this lineage in almost similar frequency. Our study shows the presence of YAP+ve lineage in North Indian populations, reflecting an African/Middle Eastern migration into North India.

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Phylogenetic Analysis of Major African Genotype (Af2) of JC Virus: Implications for Origin and Dispersals of Modern Africans

Both mtDNA and the Y chromosome have been used to investigate how modern humans dispersed within and out of Africa. This issue can also be studied using the JC virus (JCV) genotype, a novel marker with which to trace human migrations. Africa is mainly occupied by two genotypes of JCV, designated Af1 and Af2. Af1 is localized to central/western Africa, while Af2 is spread throughout Africa and in neighboring areas of Asia and Europe. It was recently suggested that Af1 represents the ancestral type of JCV, which agrees with the African origin of modern humans. To better understand the origin of modern Africans, we examined the phylogenetic relationships among Af2 isolates worldwide. A neighbor-joining phylogenetic tree was constructed based on the complete JCV DNA sequences of 51 Af2 isolates from Africa and neighboring areas. According to the resultant tree, Af2 isolates diverged into two major clusters, designated Af2-a and -b, with high bootstrap probabilities. Af2-a contained isolates mainly from South Africa, while Af2-b contained those from the other parts of Africa and neighboring regions of Asia and Europe. These findings suggest that Af2-carrying Africans diverged into two groups, one carrying Af2-a and the other carrying Af2-b; and that the former moved to southern Africa, while the latter dispersed throughout Africa and to neighboring regions of Asia and Europe. The present findings are discussed with reference to relevant findings in genetic and linguistic studies.

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