Determining half-relationships with Polynesians – Part II

In my last entry I demonstrated the difficulties of determining the half-relationships after receiving the DNA results of my half-first cousin.   Within an endogamous group, that could be even more difficult as we see larger amounts of DNA shared.

While the ISOGG Wiki Autosomal DNA Statistic page can list the average amount of centimorgans shared,  Blaine Bettinger’s The Shared cM Project  demonstrated that the minimum and maximum amounts shared can vary.  This becomes more evident as the distance of relationship increases.

Within an endogamous group it makes sense that having more than one pair of common ancestors may increase that amount.  The same would apply if you descend from the same common ancestor multiple times.  Both would produce higher amounts shared.

A few months ago I got the results of my aunt believed to be a full-sister of my mother.  My aunt suspected that her father was not her biological father.  And she was right.  But she was not the only one who knew of this, but the rest of the family, particularly the ones of my generations believed that this Aunt’s father was her biological father and did not suspect otherwise.

From my mother’s Family Finder (autosomal) match list at FTDNA:

Screen Shot 2016-05-03 at 5.21.34 PM

The top is my mother’s sister while the one right below it belongs to my half-1st cousin whose father George was mentioned in the last entry – Determining half-relationships with Polynesians.

Initially I was confused by the total amount since I knew it was more than what I shared with two of my half-brothers.  This is how two of my half-brothers compare to me and to each other.

Screen Shot 2016-05-03 at 5.47.08 PM

So my mother and her sister did share a bit on the high-end for half-siblings, but low end for full-siblings.  These are the predicted averages shared for siblings vs. half-siblings.

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The next step was to take a look at the X chromosome.  For half-sisters who had the same father, they would share an entire X chromosome based on how the X is inherited.  To my surprise, it looked like someone took a razor blade and sliced out some pieces of the image.

 

5+cM setting

5+cM setting

 

1+cM

1+cM

For half-sisters they share a lot compared to what I saw when comparing my half-brothers to each and to me.  Also, I decided to include both the default 5+cM setting and the 1+cM.  With my brothers, we hardly get anything when I lower it to 1+cM.  But with my mother and aunt, you can see a difference although chromosomes 4 and 18 are more likely to be IBS, but given the situation (endogamy, small communities, & isolation) it just may be IBD from a very long time ago.

So the X was not helping me one bit since I thought maybe they were areas on the chromosome that could not be read – no calls.

I immediately uploaded to GEDmatch for further analysis.  No surprise that when I looked at the X, it was the same exact thing.   Knowing that it wouldn’t be helpful, I turned to the other 22 pairs of chromosomes.

Screen Shot 2016-05-03 at 6.52.44 PM

What you would be looking for in full-siblings are full-identical regions (FIR) which are the green sections on the bar graph.  Here is an example of my 1st cousins, a brother and sister.

Screen Shot 2016-05-03 at 7.55.59 PMScreen Shot 2016-05-03 at 7.56.08 PM

About 25% will be fully identical.  You can read more about how much full versus half-identical regions siblings would share at ISOGG’s Wiki – Fully Identical Region page.

This is what my mother and aunt showed.

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There are only small chunks of  FIR rather than long segments of it that you would see in full-siblings.  So this confirms a half-sibling relationship.

Small segments on the X; male vs. female

Kitty Cooper put out a blog post where she entitled it What Can the X Chromosome Tell Us About the Importance of Small Segments? by Kathy Johnson.   Kathy Johnson had gone through the males in her project and began analyzing and compared to females, determining how much of the females were producing false positives vs. the men.  Because not many men would get a lot of X-matches.  This seems to be an ongoing investigation with various people blogging about the validity of phasing, or rather how effective if not necessarily is it to weed out any false positive matches. It seems to be based on FamilyTreeDNA’s X-matches where they include many tiny segments as little as 1cM.  And the more substantial matches with 10cM or more tends to reduce the actual X-matches significantly, which would be due to the lack of phasing.  You can read more about it on Kitty’s blog, although most of the discussion about evaluating all of these matches took place outside of the blog and on Facebook’s “International Society of Genetic Genealogy” page.

That made me curious, because others have expressed how some men had little to no X-matches.  This was not my situation at all , and went through my list of 9 pages on FTDNA and counted 47 X-matches out of the total 89 matches that I have.  I noticed that one of them was actually an X match on my father’s side of matches, a Filipino.  I knew that was wrong.  So when I looked at it, no X match showed up in the chromosome browser until I reduced the threshold down to 1+cM where I saw a 1.9cM, a false match.

Aside from one woman mislabeled as a male in my matches, I actually have 20 men and 26 females as X-matches, not counting that Filipino false match.  That’s half of my matches.  My mother has 93 X-matches out of her 159 matches, so not that much more than me.  Could that indicate that my mother’s X-matches are more, or less of false matches?  It’s an interesting idea to see how men can have less false matches but we are looking at Polynesian matches which just adds something else to it.

I know that I do have a lot of my matches below 5cM on the X chromosome, so I used dnagedcom.com’s ADSA (autosomal DNA segment analyzer) to at least look at my ICW (in common with) matches on the X, but I had increased the threshold to 700SNPs and 10cM.

Screen Shot 2014-12-20 at 12.30.11 PM

I was thinking that not only would it be easier to use this tool by instantly seeing my X-matches above a specific threshold, but it would also compare me with others with whom we share the same segments, therefore decreasing the chances of false matches.  But taking into consideration that we are referring to Polynesians.  How would that affect it really?

I cannot determine from comparing my own to my mother’s X-matches if they would be false matches or not. Our problem, lack of documentation, lack of genetic diversity and the unpredictability of the X chromosome itself just to mention a few.

I have recently begun testing my first cousins on my non-Hawaiian side in order to take a closer look at the X chromosome and how that is passed on knowing the X path, that is how it is passed on unrecombined from father to daughter versus mother to children.  I also felt that knowing how it is passed on, it would be easier to distinguish which part of the chromosome was inherited from my grandfather versus my grandmother.  And not until I begin testing relatives from each of my grandparents’ side, I will not be able to fully distinguish all of them with the rest of the other 22 pairs of chromosomes.

Having said that, I cannot see how these X-matches, at least among Polynesians would be consist of a lot of false segments or not.  Especially when there are long segments with the more distant people, e.g., Maoris or Samoans and Tongans, of which I do have X matches with.  But the Samoans and Tongans are not included in the ICW due to the fact that I increased the threshold to exclude anything below 10cM.

I also used Gedmatch’s ONE TO MANY to get all my matches, sorted them by the largest segment on the X and just looked at how many were above 10cM.  There were only 20.

Screen Shot 2014-12-20 at 8.21.57 PM

I did the same for my brother, he got 17 above 10cM.  I also looked at other Polynesian men just to compare and the numbers varied, usually not exceeding 20 with 10cM minimum threshold.  It is still all interesting although it is hard to decipher how much of it is true for Polynesians.  Hopefully as more Polynesians get tested, we will start to notice more differences, or confirm that we just all have a high amount of X-matches.

Runs of Homozygosity – Are your parents related?

On Gedmatch there is a tool where you can run your raw data and it can determine if your parents are related by looking for strands of homozygous DNA.  Better known as “runs of homozygosity”, or ROH,  are regions of the genome that are identical because you inherited an identical copy from each parent which would indicate that there was a common ancestor.  This will create a run of homozygous variants.  ROH

ROH are informative.  The longer runs obviously tells us that there was intermarriage while short runs of ROH have the potential of informing of population history, i.e., populations that have gone through a bottleneck followed by a period of intense inbreeding that will result in long runs of ROH.  Then as time passes these long runs become to look like patches throughout an individual’s genome, showing both homozygous and heterozygous regions.

The sporadic placement of these long ROH on various chromosomes are consistent with bottleneck populations.  In Razib Khan’s blog he has an entry about how not all homozygosity is created the same.  He refers to a paper that mentions how when looking at various world populations, there was obviously a difference.  In certain areas, these long ROH was attested to cultural patterns of inbreeding, as well as small population size.  Short and medium ROH are results of bottleneck, and smaller effective population while long ROH is due to effective population size which occurs during inbreeding.

So looking at how this would affect Polynesians, I started analyzing all of this and predicting what I would see.  Since Polynesians lack genetic diversity, but knowing that eastern Polynesians (Hawaiians and Maoris to name just a couple) are less diverse than western Polynesians (Samoans and Tongans), due to the migration patterns of ancient Polynesians from west to east, I would probably see less ROH, depending on the island population, with western Polynesians versus eastern Polynesians.

I tried this tool months ago a few times but it looked like it was not working properly or the results just was not easily understandable.  I tried it again and now they break it down by each chromosome showing you how much and where these runs occur, using the minimum criteria of 7 centimorgans.

Analyzing my own mother’s results seemed to have a decent amount of ROH, specified below by total shared, largest segment and on which specific chromosomes these were found.  The largest segment was 13.9cM, the estimated number of generations to the MRCA (most recent common ancestor) is 4.1.

ROH-mom01

ROH-mom02

My mother showed that she has at least 5 chromosomes that showed ROH, the largest segment being 13.9cM, the smallest segment 7.5cM.  Another Hawaiian showed 6 chromosomes, largest segment 22.4cM, and a total of 8 segments, 3 of those segments are on one chromosome.

After going through my mother’s matches (from her ONE TO MANY) and looking at Hawaiians, Maoris of New Zealand, Samoans and a half Tongan, I definitely saw a pattern.  A couple of Maoris that did show ROH showed 2 to 3 chromosomes that had ROH, with the largest segment as large as 16.6cM, and as small as 7.1cM.  I was only able to find one Samoan woman out of the 5 known Samoan matches to my mother that had at least 2 chromosomes that showed ROH.  Her largest segment however was only 8.8cM.

This seems consistent with the research as well as the known history of the populating of Polynesia.  Hawaiians have gone through a recent bottleneck at the end of the 19th century and have recovered from that.  So it is no surprise that Hawaiians and Maoris would show more ROH than Samoans or Tongans.  More so with a population expansion after a bottleneck effect we do see how Hawaiians not only show more of ROH but it also appears to be sporadic throughout with both short and long ROH, as in one Hawaiian’s example he has 3 segments of long ROH that were on one chromosome.

GedMatch’s Full Matching Base Pairs

Kitty Cooper had a blog entry – “When is a DNA segment match a real match? IBD or IBS or IBC?” that discussed a problem when it comes to matches, some of these are not true matches due to the fact that when we share a matching segment with someone of a common ancestor, it is based on half identical regions.  We basically get a set of alleles from each parent but genome testing looks for stretches of DNA, however it cannot figure out whether it came from your father or mother.  This is what can cause problems with matches because they may not be a true match.  More about this can be found here:
http://dna-footprints.com/203/the-abcs-of-dna-ibd-vs-ibs/
http://dna-explained.com/2012/09/03/matches-family-ibd-vs-population-ibs/

When doing a ONE TO ONE comparison on GedMatch.com, you have the option to show a graphical bar for each chromosome that is color coded and it can show where on a chromosome you match half of the base pairs, or have a full match.  Usually the full matches are seen when being compared to siblings.  Parts of it will be green, the other yellow, and also red.  When compared to an identical twin, it will be all green.

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This is what it looks like when comparing my kit to my half-brother’s.  Below are only a few of the chromosomes where we match, but you can see where the blue is under the yellow.  Blue indicates that the segments are at least 7cM and the yellow indicates that it is a half match base pair.

Screen Shot 2014-11-06 at 6.57.56 PM

 

Since Polynesian are super endogamous, resulting from successive founding populations and bottle necking events, it is not unusual to see full matching base pairs in green.  Below is what it looks like when comparing my mother to my friend’s father.

mom-lawrence-GREEN-compare

I am only showing four of the chromosomes, the chromsomes that had the most full base pair matches.

We are not close relatives, but my mother does share a lot with him.  These are the segments shared between my friend’s father and my mother.  Only chromosomes 1 and 3 show no green segments.  All the others do have green segments.

mom-lawrence-segments

What this means is that both pairs of each chromosomes are matching.  So my mother’s parents and my friend’s paternal grandparents were all related.  When doing a ONE TO ONE comparison, it is usually easier to compare without the graphs, unless you are looking for something specific, like with identical twins or full versus half-siblings. In the case of endogamy however, it may or may not be useful, depending on what you are looking for.  If you are simply looking for a match, then it is not needed.  I wrote in a previous blog entry about multiple small segments as a key for endogamy, using a graph may give a better insight with how much you may be related to someone, or rather how many times you may descend from common ancestors.

Although I have not made an in-depth comparison yet, but from what I can tell it seems that the majority of the green bars indicating a full base pair match is more noticeable when comparing my mother with other Hawaiians.  I compared all the known Maori matches who share more totals with my mother versus Hawaiians who do not share as much, and from what I can see is that they do show a few tiny green segments.  The most obvious is that the less admixed the Polynesian,  the easier it is to see more green segments.  This makes logical sense and of course the amount of green would be more indicative of ties to a specific geographic area, or rather indicate that people have remained in a specific geographic area for a longer amount of time.  This too should be obvious by the multiple number of segments.

So to summarize, the full base pairs (green) means that there are multiple lines of relationship, more specifically to the parents of the matches if the amount of green segments are large or nearly matches the blue bar indicating matching segments great than 7cM.  While the multiple segments would indicate descending from a common ancestor multiple times.