Tag Archive | DNA segment match

Finding a relationship with DNA segment data

Ancestry has spoiled us all with its tree and ancestor matching tools; so much so that I almost never look at the actual segment data any more. Ancestry does not provide that anyway. When autosomal DNA testing first came out, you had to look at the segments on each chromosome that you shared with your matches in order to figure out relationships. Personally, I kept a master spreadsheet of DNA segment data for all my Dad’s matches from the different sites (click here for the post on how to do that or here for all the posts on that topic).

Comparison of my father to various Fatland cousins at Family Tree DNA, names added by me

The raw DNA data from Ancestry can be uploaded to a number of other sites in order to do chromosome comparisons and see the segment information: GEDmatch, Family Tree DNA ( ftDNA), and MyHeritage. You can see if you have good matches on those other sites without paying, but to unlock them on the latter two sites will cost a small amount. GEDmatch is free but it has extra tools that are available for a nominal charge and of course it can be used by law enforcement if you have opted in. Please do so and watch Cece Moore on the TV show the Genetic Detective to see why!

How is the segment data useful? It helps when you have many segments assigned to specific ancestors because of who they are matching with. Then when a new DNA relative appears you can figure out which line they are related on based on their shared segments with you and your relatives. Many people prefer to use the chromosome painting capability at DNApainter rather than spreadsheets to keep track of segments. I have been keeping my Dad’s sheet since 2011 so it’s just easier for me to add new relatives there.

I recently noticed that Dad had a 33.5 cM single segment match (I do not include the many segments less 7cM) on Family Tree DNA to a Norwegian named Jan Olav Risvold (who gave me permission to use his full name). Normally I ignore single segments, but this one was large and fell in a section of chromosome 2 which is well mapped for my Dad, so I took a look. Also Vold (Wold) is a family name, so perhaps?

Screenshot of Dad’s master spreadsheet with segment data, Jan is the first line, colored by side

One problem with segment data is that you cannot tell which side it is from without other relatives to compare to. Luckily for us, my brother and I have often inherited different segments at the same location from our Norwegian-American Dad. Therefore by comparing them to other cousins we can tell whether they are from his mom or his dad. Jan matches my brother on that segment but not me. Thanks to a 6th cousin, Frode, who shares 22cM at the same location with my brother and dad (see image at the top of this article), we had previously identified the ancestral couple that this DNA came to us from, our Fatland 5th grandparents, Ole (1696-1772) and Brita. on Halsnøy Island in Hordaland. They are our ancestors via Dad’s maternal grandad Henry H. Lee from Skjold farm in Etne, Hordaland.

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Size Matters for Matching DNA Segments

The more large segments you share, the more closely related you are to a DNA match. To learn more about segments, read the blog by one of my favorite DNA writers on the yahoo DNA-NEWBIE list, Jim Bartlett, called Segmentology.org
Brynne Ancestor MapHe explains why you share such large chunks of DNA with your closer relatives by showing how recombination works and how few cross-overs there usually are in a recent post at  http://segmentology.org/2015/05/24/segments-bottom-up/

While the total amount of shared DNA in centimorgans (cMs) is a fine indicator for your closest relatives out to second cousins, farther relationships can be more and more random in the amount of shared DNA. You can consult the charts and numbers at ISOGG here – http://www.isogg.org/wiki/Autosomal_DNA_statistics – to determine those closer relatives.

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Using your DNA test results: the Basics for Genealogists

How do you use autosomal DNA testing to enhance your genealogical research without having to take a PhD level course? This is a question several of my cousins have asked me, so here is my attempt to answer.

KittyTopMatchesMap

Chromosome Map of Kitty’s Closest Matches using her segment mapper tool

  • First of all, get as many relatives to test as you can. The more data you have, the easier it is to make useful comparisons and sort new DNA relatives into their related family lines. The closer family members shown in my chromosome map above are all cousins I convinced to test.
  • Secondly, make sure you know how to use a spreadsheet: sorting, deleting rows, inserting columns; you only need to know the easy stuff. [UPDATE: click here for my post with a youtube video teaching that easy spreadsheet stuff]
  • Third, check your understanding of how DNA works. Perhaps read my basics page – http://blog.kittycooper.com/2013/04/the-basics-at-23andme/ – and follow up with whichever lessons, books or videos appeal to you among those that I suggest or that you find listed in the ISOGG wiki – http://www.isogg.org/wiki/Autosomal_DNA
    Also lots of beginner questions are answered in the FAQ I keep for the DNA-NEWBIES mailing list on yahoo; a copy is on this blog – http://blog.kittycooper.com/dna-testing/newbie-faq/ – so check there when something is confusing.
  • Fourth, bookmark a page with an explanation of all the acronyms – this is a good one: http://www.isogg.org/wiki/Abbreviations – a key term is cM. You do not need to understand the definition of a centimorgan (cM), hardly anyone does; just accept that it is the best measure of the importance of a DNA match, the larger the better.

Now to the practical application of all this, using shared DNA segment data to find relatives, preferably those 3rd and 4th cousins that your family no longer knows of. Click on success stories on this blog to read about some of the cousins I have found with DNA.

When people are shown as matches to you or your relatives, the testing company will make a guess as to how closely related they are. Beyond 3rd cousins, it is not possible for them to make an accurate estimate because of the random nature of DNA inheritance.

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How is it that I share such a large DNA segment with so distant a cousin?

I recently posted this insight to the DNA-NEWBIE mailing list.

I have found it interesting that I share fairly large segments with a 10th and a 14th cousin but none with a 4th cousin that my Dad does share DNA with. Norwegian records are good so all these cousins have good paper trails. i did notice that we all come from many generations of large families…

This blog article offers a good mathematical explanation of this phenominum.

http://ongenetics.blogspot.com/2011/02/genetic-genealogy-and-single-segment.html?m=1