Loss of heterozygosity – from Western Polynesia to Eastern Polynesia

Genetic research on Polynesians will frequently mention the loss of heterozygosity.  This is more noticeable when comparing eastern Polynesians to western Polynesians.

oceania

Map outlining migratory paths of Austronesian speaking populations, including estimated dates. Adapted from Bellwood et al., (2011) “Are ‘Cultures’ Inherited? Multidisciplinary Perspectives on the Origins and Migrations of Austronesian-Speaking Peoples Prior to 1000 BC.” [doi: 10.137/journal.pone.0035026.g001

Polynesian populations are relatively homogenous both phenotypically and genetically. Over a span of 3,200 years they moved throughout the Pacific, and unlike in Europe and other large continents, they did not mix with other populations due to isolation.  These small founder populations have experienced several bottleneck effects, which further caused this loss of heterozygosity ending with the settlement of eastern Polynesia.  Polynesians’ lack of genetic diversity is less evident in western  Polynesia where initial settlement began.  Hawai’i, New Zealand and Easter Island are considered to be eastern Polynesia, and these places were the last places of Polynesia to be settled.

Recently I have been able to look at the autosomal matches among Samoans and Tongans of western Polynesia.  Previously, I have been only studying Hawaiian matches and noticed that top matches were both Hawaiians and Maori people.  Looking at Samoans and Tongans was very interesting as I now could compare the two different regions.

My mother is 80% Hawaiian, while I am 40%.  And as admixed as I am, I still get 1st – 3rd cousin predictions on Family Tree DNA (FTDNA), while on 23andme I get 2nd cousin and 3rd to distant cousin predictions.  The centimorgan totals that I show with my matches reach as high as 369cM on FTDNA, and 161cM on 23andme.  For my mother, 693cM on FTDNA and 376cM on 23andme.  I see the same happening with Maoris, ranging between 300cM – 700cM (FTDNA) for the top 20 people.  And for a non-admixed Hawaiian, their top matches are in the 600 – 700cM range.   An admixed Polynesian would logically have lower totals. But even an admixed person can still have a fairly high amount of totals shared, as when I am comparing myself being less than half Hawaiian.

When comparing two Tongans, the highest that they shared was 335cM.   A Samoan compared to another Samoan was 366cM.  And both of these Tongans and Samoans had their remaining top matches in the range of 100cM to 200cM.  Many of their matches are the same Hawaiians and Maori that match each other at a much higher total.  It is amazing to see these autosomal matches and how diverse the western Polynesians are, or rather how Hawaiians and Maoris are not as diverse.  And even if it is an admixed Hawaiian or Maori, the matches to each other are still pretty high, and as high as what non-admixed western Polynesians would have to each other.

When comparing the longest block (largest segment) with Tongans and Samoans, they seem to rarely get close to 15cM, averaging around 10cM.  Anything more than that could indicate a possible closer relationship or perhaps a specific common geographic origin.  The Hawaiians and Maoris usually range between 10cM – 15cM for the largest segment, but can go as high as 28cM which is usually in admixed Hawaiians and Maoris compared to each other.  In other words, all Polynesians in general will have high totals exceeding 100cM, but whose largest segment rarely exceeding 10cM.

I look forward to more western Polynesians getting tested so we can see if there is any pattern to specific islands in their own island group, something I have been trying to do with Hawaiians with the few haplogroups that there are for Polynesians.  What also needs to be analyzed are people from Tahiti and the Marquesas being that they were key dispersal points for eastern Polynesians.  I managed to only see the results of one admixed Tahitian woman and her match totals are identical to mine when comparing totals.  I am curious to find out what non-admixed Tahitians will show, if it is more identical to eastern Polynesians, or to western Polynesians.

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