Extremt gammal variant av gen funnen hos Papuaner
Forskare har funnit ovanligt hög mångfald i genen OAS1 hos Papuaner. Mångfalden är större än hos afrikaner. Detta har orsakats av blandning med arkaiska människor.
Den gemensamma förfadern till den arkaiska haplotypen och den afrikanska (moderna) haplotypen uppskattas ha levt för mer än tre miljoner år sedan. Det är mer än människosläktet Homos tid på Jorden.
Tidsberäkningar är alltid mycket osäkra men man kan slå fast att haplotypen är arkaisk. Vi vet att melanesier och aboriginer har blandat sig med denisovamänniskor. Omkring 5% av generna kommer från denisovamänniskan.
Abstract:
Recent analysis of DNA extracted from two Eurasian forms of archaic human show that more genetic variants are shared with humans currently living in Eurasia than with anatomically modern humans in sub-Saharan Africa. While these genome-wide average measures of genetic similarity are consistent with the hypothesis of archaic admixture in Eurasia, analyses of individual loci exhibiting the signal of archaic introgression are needed to test alternative hypotheses and investigate the admixture process. Here, we provide a detailed sequence analysis of the innate immune gene, OAS1, a locus with a divergent Melanesian haplotype that is very similar to the Denisova sequence from the Altai region of Siberia. We re-sequenced a 7 kb region encompassing the OAS1 gene in 88 individuals from 6 Old World populations (San, Biaka, Mandenka, French Basque, Han Chinese, and Papua New Guineans) and discovered previously unknown and ancient genetic variation. The 5′ region of this gene has unusual patterns of diversity, including 1) higher levels of nucleotide diversity in Papuans than in sub-Saharan Africans, 2) very deep ancestry with an estimated time to the most recent common ancestor of >3 million years, and 3) a basal branching pattern with Papuan individuals on either side of the rooted network. A global geographic survey of >1500 individuals showed that the divergent Papuan haplotype is nearly restricted to populations from eastern Indonesia and Melanesia. Polymorphic sites within this haplotype are shared with the draft Denisova genome over a span of ∼90 kb and are associated with an extended block of linkage disequilibrium, supporting the hypothesis that this haplotype introgressed from an archaic source that likely lived in Eurasia.
