Thursday, January 24, 2008

More on the pacific islanders

Thought I would pop a couple of pictures up from the Pacific island paper , and briefly point out another paper on the topic. One of the debates that the paper sought to resolve is "Are Polynesians more closely related to Asian/Taiwanese populations or to Melanesians?"

First a picture of the area (taken and cropped from the PLoS genetics paper, citation at the bottom), as I had trouble remembering what populations are where

the Polynesian/Micronesian populations (on this map) are the Maori, Samoans and the Micronesians. Previous mtDNA work had suggested that the Polynesians were closely related to each other, supporting the proposal of a 'express-train to Polynesia', that these people moved rapidly (by boat) out from Taiwan, around the surrounding islands (with little contact with the people of these islands) before reaching their current locations. Others had suggested on the basis of the Y chromosome a 'slow boat to Polynesia', with the Polynesian populations mixing with Melanesians along the way.

Here's a pictures (from the paper) of the output of the program Structure (the top panel is individual ancestry, the bottom panel is ancestry averaged in within each population (mainly to aid the eye)). The Structure analysis is in this case constructing the Micro/Polynesian individuals (the last columns) as mixtures of the 8 populations (solid colors, purple Taiwanese, turquoise East Asian, Green: Kuot (Papua New Guinea).)

I've shown this picture (from the supplementary files of the paper) rather than one from the main text (shown just below) as it more clearly shows (well apart from the blurriness, sorry) that Polynesians are more closely related to aboriginal Taiwanese (and not the rest of Asia) with only a fraction of Melanesian admixture. There are also trees in the paper (constructed from Fst) that support the conclusions of this picture (they also show that the Maori seem to have been through quite a bottleneck).

another paper (in ASHG this time) looking at a large number of microsatellites in Polynesians (also with data from Melanesians and Han Chinese). This paper also estimates that while the Polynesians are closer to Mainland Asians (Han in their sample) than to Melanesians, Melanesians made a substantial genetic contributions to the Polynesians. They perform this analysis in a more formal population genetics setting than the PLoS genetics, to estimate the ancestral proportions of Polynesian population contributed by the two parental populations (Han and Melanesian) in a framework that allows for genetic drift. This is in agreement with the PLoS genetics paper, though I do wonder about the use of the Han as the parental population, as the results of the PLoS genetics paper indicates that aboriginal Taiwanese are closer to the Polynesians than the rest of Asia.

Friedlaender JS, Friedlaender FR, Reed FA, Kidd KK, Kidd JR, Chambers GK, Lea RA, Loo JH, Koki G, Hodgson JA, Merriwether DA, Weber JL.
Free in PMC
The Genetic Structure of Pacific Islanders.
PLoS Genet. 2008 Jan 18;4(1):e19

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