Determining half-relationships with Polynesians

I recently got my cousin’s results to compare to my mother and my brothers.  This cousin’s father was my mother’s half-brother George, so a half-first cousin relationship.

Prior to making contact with my mother’s relatives I was thinking of having these cousins tested as a means to figure out who my mother’s biological father really was.  But a couple of months ago when I did make contact with these long lost relatives it was revealed that my mother’s biological father was Joseph Kaapuiki Akana, the man whom I doubted was my mother’s father based on his name (Akana is of Chinese origin) and the fact that my mother remembers her father being pure Hawaiian and her DNA composition does not support Chinese ancestry.  I thought that maybe testing these half-cousins would determine if their grandfather was my mother’s biological father.  But it is more complicated than I realized.

Like my mother’s father Joseph Kaapuiki Akana, George’s father was also Hawaiian.  George and my mother shared the same Hawaiian mother.

This is what the ISOGG Wiki Autosomal DNA Statistics page says about how much should be shared between a half-aunt and also to half-cousins.

Screen Shot 2015-12-29 at 7.17.17 PM

Combining with Blaine Bettinger’s Shared cM Project, the total shared for a half-aunt would range from 540cM to 1348cM, averaging 892cM.  The average is around the amount indicated by the ISOGG Wiki page.

For a half-first cousin, Blaine Bettinger’s Shared cM Project says it would range from 262cM to 1194cM, averaging 458cM.  Again, that average is what is indicated on the ISOGG Wiki page.

This is how GEDmatch.com compares my half-cousin to us.

Screen Shot 2015-12-29 at 7.33.09 PMIt is obviously on the high end, for a half-aunt while half-first cousin, not that extreme.  But we are talking of one example only.  There are more half-cousins that I could have test and probably will in the future.  And all of these cousins have had a grandfather that was Hawaiian, so I would expect their amounts to be high.

Comparing to non-endogamous groups, I compare my paternal aunt to her nephews and nieces and a great-nephew and great-niece on GEDmatch.

Screen Shot 2015-12-29 at 7.45.46 PM

My cousin Terri may share the lowest total among the 1st cousins but it does not seem that significantly different from the average 1700cM.  It is interesting to see that her largest segment is 104.7cM.  When I look at my half-first cousin and how much she shares with her half-aunt (my mother), the total is 1412.8cM, and largest segment is 103.3cM.  That figure can be misleading.  I have more cousins on my father’s side that I have yet to test and there may be other cousins who share less or more with our aunt than the cousins that have already tested.

If I take my aunt out of the equation, this is how the cousins compare to each other.

Screen Shot 2015-12-29 at 7.50.04 PM

A couple of my paternal 1st cousins share much less with each other than my half-cousin does with me and my brothers.

It will be awhile before I can get an ample amount of Polynesians who have close relatives tested to fully make a comparison.  Initially I wanted to see if testing half-cousins would help determine if my mother’s siblings were half or full siblings and when I was not certain that Joseph Kaapuiki Akana was her biological father.

It is clear now that any type of half-relationship is difficult to determine if the other parent is also Polynesian, and in our case Hawaiian.  My grandmother married 3 different Hawaiian men and so far from what I know, they have ties to geographically different places.

The endogamous nature just makes it hard to determine the relationship even if it is a close relationship.  It does not have to be a distant 3rd cousin and beyond to appear as a closer relationship.  Even with cousins (half or full) and half-siblings, they seem to appear on the higher end of the relationship, possibly giving a false prediction if the true relationship was not known.

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