Down the DNA Rabbit Hole

I spend much of my genealogy work these days trying to sort and analyze my DNA research. It is amazing how time consuming this aspect of genealogy can be. However, I find it very fulfilling as well as enlightening. Currently I am working on a project that I think will break down several brick walls. As much as I want to share (because I am excited!!!), I also need to find two good cases to use for my BCG portfolio.

For the last year, many people in the genetic genealogy community have been very excited over a technique using the autosomal DNA of three of more siblings to map their chromosomes. In the beginning, I was stymied by this technique as I have only one sibling. However, I have used the shared DNA of my close family relatives to supplement the “three-sibling technique.”

Why is chromosome mapping important? For me, I love the visual picture of the map. Additionally, and most importantly, the map shows valuable information that I can use when tracing unknown matches. Below is an example of a mapped chromosome.

The top color block shows a one-to-one comparison of my brother and myself from the gedmatch website. The dark blue blocks show where we share half of our DNA while the gray sections indicate where no DNA is shared at all. A small section of bright green between lines 28-31 denotes that my brother and I inherited identical DNA from both our parents. Remember each chromosome is a pair (we inherit one from each parent).

The middle block is a representation of the segments I inherited from each of my four grandparents. The third block paints the segments of my brother’s thirteenth chromosome. I was able to complete this chromosome map thanks to five first and second cousins as well as several more distant cousins who have tested their autosomal DNA. By tracking and comparing the locations of shared segments among the cousins, I was able to determine which segments of DNA my brother and I inherited. Tracking is easily done with a basic spreadsheet.

My known paternal matches on chromosome 13

For future research, the completed map becomes a valuable tool. Whenever a match shares a portion of this chromosome with me or my brother, I can identify which branch of the family the match comes from. I can also use future matches to test the validity of the chromosome map.

©2017 Deborah Sweeney
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9 thoughts on “Down the DNA Rabbit Hole

  1. davidmadison1942

    thegenealogygirl said it: “I barely understand it, but I love it.” My science aptitude hovers close to zero (although I enjoy reading the history of science), so it’s cool that you have a grasp of these things. 🙂

  2. cassmob

    It gets even tougher when neither you nor a parent has siblings, so you’re totally reliant on 2nd cousins for that branch. I need to play more with mapping.

    1. Deborah Sweeney Post author

      There is a discussion going on today on the Genetic Genealogy Tips & Techniques FB group about how second cousins are great people to have test. I currently have five second cousins who have tested. They are great people to test!

    2. Deborah Sweeney Post author

      And I definitely agree with you on the no siblings! My grandmother was an only child, plus her maternal uncle had no children. I really struggle with finding ways to map her side of the tree.

    1. Deborah Sweeney Post author

      Just keep reading and following the DNA group pages. It will make sense eventually. I attend the DNA day at Jamboree every year (this will be my third year) plus I sign up for DNA workshops when I can.
      I’ve been using the Maguire chart technique the last couple of months and I have learned a lot from my data and matches just by trying a new way of organizing my data.


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