|Big time triangulation|
When I first took the Family Tree DNA, Family Finder autosomal DNA test, I had no idea how I could use the segment information to prove my matches. It seemed very complicated. I quickly found out the mechanics of it weren't that complicated at all, and it's necessary to prove relationships with cousins.
The first cousin I confirmed through DNA was a 5th cousin I had been collaborating with for several years. We could be fairly certain our segments came from our paper trail lines because we don't appear to have any other relationship according to our trees. When my Mom tested and shared the same segments we knew for certain they were IBD through my maternal line. We also could be sure we were not related through my mother's maternal side which is Nicaraguan, and my cousin has no Nicaraguan ancestry.
When examining the segment information for my 5th cousin we notice she shares more than one segment. I have found if someone shares more than one segment, including one over 10 cM's, and the others about 5 cM's or over, a relationship within the past 6 generations generally can be found. Also my 5th cousin has had her brother and aunt tested adding confidence to the IBD segments. We can see her brother shares a 5 cM segment which is IBD because 4 of us share on the same segment, and the others segments are in the high confidence, IBD size, range. All of us sharing these particular segments are descended from double first cousins. So we cannot say from which ancestral couple we received these segments? If we can find other cousins who match on these segments and they are not in our double first cousin line we could then say we got these segments from a particular ancestral couple.
|Matrix showing nearly |
|Triangulation of matches |
from the same area in Ireland
The Nicaraguan matches don't usually have exact locations in Nicaragua. I know my family is from Granada, Nicaragua, so I keep an eye out for those matches. My Grandmother Graciela Del Castillo-Forgey had a number of Nicaraguan friends. I am familiar with their surnames, and I'm finding those names in our matches, names such as Lacayo and Chamorro. According to my Grandmother first cousins often married in Nicaragua so it may be difficult to separate out these DNA segments due to so much intermarriage. This may also be true on my Irish side, because the population was small in our ancestral locations. My family came from the Townland of Pollaturick in Galway, Ireland, and the Townland of Kilvine in Mayo, Ireland. I find it rewarding when my matches ancestors come from the same small area of Ireland as my family. I have a triangulation with several matches from the same small area of Ireland. Since most genealogical relevant records for Ireland have been destroyed I don't expect we'll ever find the names of the ancestors who passed these segments down to us. It's great to have the ancestral locations confirmed through DNA anyway.
|Itty bitty Owens segment. An unnamed company would call this a moderate match??|
When it comes to brickwall lines and segments I haven't been able to use the segment data, yet, to absolutely prove a relationship. We need more segment matches to add weight to our paper trail inferences. Right now I only have segment data for single segment in a particularly challenging brickwall line. I have brickwall related matches at fill-in-the-blank -------- Company. They don't provide segment data. So I have no segment data on for these matches, I won't be able to triangulate or confirm these matches. The segment I have is only 5 cM's, which I can't be confident is IBD. It would be great to find more and larger segments, and triangulation on the brickwall lines.
How segment data has helped me:
- They've provided actual proof that I'm related to a cousin. Without having the segment information there is no proof you are related to anyone. If a company provides you with a list of match names it's meaningless. We need to cite the DNA evidence like we cite documentation on our tree. We need to cite numbers and chromosomes. Not having this information is like only looking at an index to records without seeing the actual records. You don't have possession of the evidence without segment data.
- I've been able to infer, then prove, a relationship with several matches based on matching on the same segments. Some of these people didn't have trees. When I emailed them they would often confirm the relationship through a particular line.
- The segment information allows me to evaluate which matches are the most promising for further study; such as those sharing more than one segment.
- Segment comparison in an endogamous population is not useful at this time. It only works well in mixed populations where there are more differences in the DNA
- Many of us with Early American ancestry find a web of relationships among our matches which is hard to untangle. If you test enough family members this can often be over come.
- Segments under 5 cM tend to be IBS and should not be used to draw conclusions. Some people are unaware of what the differences in segment size mean, and draw conclusions using IBS segments.
I've been able to work the DNA results by dividing them into piles based on ancestral locations. My family has such a varied ethnic heritage, making this possible. I can also divide matches by my maternal and paternal sides, because my Mom tested. My Mom's line can be divided in half because her mother was Nicaraguan, and her father was Northern European American. If I find a Nicaraguan match I can be confident it's from my Del Castillo/Garcia line. When I name segments I assign them to a couple based on the earliest shared ancestral couple on our trees.
The segment information has been the most useful, to date, in supporting my paper trails. Sometimes my paper trail is confirmed through shared ancestral names, other times it's shared places.
I have to say seeing the shared segments is rewarding. I mean actually seeing the shared segments with my own eyes. I think it's more exciting than seeing a list of match names.
Some blog posts about segments from authorities on the subject:
- "The Folly of Using Small Segments as Proof in Genealogical Research" Part One. By CeCe Moore
- "Small Matching Segments – Friend or Foe?" By Blaine Bettinger
- "Chromosome Browser War" By Roberta Estes