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Genetic Genealogy: A Powerful Tool for the Family Historian

Hidden within your DNA is the story of your family’s history, a snapshot of your ancestors and their trials and tribulations. Several companies are now helping family historians explore their DNA and unlock this hidden story in order to unravel genealogical mysteries and connect with genetic cousins.

Genetic genealogy testing first became available in 2000 with simple Y chromosome or the mitochondrial DNA tests. Just a few years ago, however, autosomal DNA tests entered the marketplace and thousands of genealogists and genomics enthusiasts have taken these tests to learn more about themselves and their past.

Humans have 23 pairs of chromosomes, including one pair of sex chromosomes (an X and a Y chromosome in males, and two X chromosomes in females). The autosomal DNA is the 22 pair of chromosomes other than the sex chromosomes, which constitutes several billion base pairs. Autosomal DNA tests examine hundreds of thousands of locations throughout these 22 chromosomes, although tests in the not-so-distant future may examine the entire genome.

The results of autosomal DNA testing can be interpreted in several different ways. For example, most companies offer an admixture analysis, which attempts to associate individual segments of the DNA with regions of the world such as Africa, Asia, Europe, and/or the Americas. The results are typically presented as percentages of the test-taker’s DNA which is believed to originate from each region.

The results of autosomal DNA testing are also used to identify genetic cousins. Testing companies will compare the test-taker’s DNA sequence to all other test-takers in the database in order to identify shared segments of DNA. Depending on the number and size of the shared segments, the company can predict a possible relationship between the genetic relatives, ranging from siblings, to grandparents, to 10th cousins.

Another very common use of autosomal testing is to explore adoption. In addition to many adoptees who are using autosomal testing to identify biological relatives, many family historians are using the tests to examine the biological roots of adopted ancestors. I’m using autosomal testing in an attempt to identify the unknown parents of my great-grandmother, Helen Johnson.

Helen Johnson was born on March 3, 1889 in upstate New York to a “Minerva D. Johnson” and unknown father. By the time she was 13, Helen had been adopted by at least three different families. Helen never learned anything about her biological parents, and in the years since her death I haven’t been able to uncover any solid leads using traditional paper records.

Two of Helen’s grandchildren, themselves first cousins, have agreed to undergo autosomal DNA testing and compare their results in order to identify which portions of their genome they share in common. Any DNA that these first cousins share will have been inherited from Helen and her husband. Armed with this information, I hope to identify others that share these portions of DNA with Helen’s grandchildren and are likely to also have descended from Helen’s ancestors. Working back with their family tree I might be able to identify Helen’s mysterious biological ancestors.

My results so far suggest that the system does indeed work. A group of genetic cousins who share a large piece of their DNA with Helen’s grandchildren appear to be related to them through Helen’s husband, Frank. Since I can’t determine which portions of the DNA that the first cousins share came from Helen and which portions came from Frank, I have to use trial and error – and my knowledge of Frank’s family tree – to weed out those genetic cousins that are related through Frank and focus on genetic cousins related through Helen. It’s a challenging process, but likely my only hope of finding Helen’s parents.

Autosomal DNA testing is a powerful new tool for family historians. When a paper trail ends or requires collaborating evidence, these new tests can reveal a wealth of information.


Blaine Bettinger edits the Journal of Genetic Genealogy. Read more about him here.

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