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Ed. Note: Autosomal DNA is a term used in genetic genealogy to describe DNA which is inherited from the autosomal chromosomes. An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X chromosome and the Y chromosome).

Each person has 23 chromosomes containing their DNA, and the DNA of each child contains a mix of the DNA of their parents. When a child is conceived, the DNA gets sliced up and mixed. You carry a roughly equal mix of DNA segments from your father and mother. But your fathers DNA is a mix of the DNA from his parents.  Each parent carried a mix from their parents who are a mix from their parents and back through the generations. Autosomal DNA analysis sequences your DNA and identifies segments of your DNA that matching segments from possible relatives. The fewer generations separating you and a match, the longer the matching segments will be. The example below is given to help you visualize how this works.

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Grandparent Chart

The top line in the family tree here represents one pair of your eight great grandparents. The colored bars represent one of the 23 pairs of chromosomes in each person. You see that their child shown on the second line has large segments of the four colors of their parents DNA. Each bar represents a stretch of DNA that contains the unique mutation signature of that parent. The third generation slices these segments into shorter segments and mixes them up still farther. But the time you get to your generation, the segments have gotten even shorter, but they can still be identified as unique to the great grandparents and grandparents and parents they came from. The blue strip is from one and the red from the other great grandparent. Each of the other ancestors would also be contributing their own unique colors which are not shown for simplicity.

The AT-DNA test identifies the unique segments in your DNA and allows them to be compared with other people in the database. Because the AT-DNA test looks at all your DNA except the Y-DNA, it opens up your entire ancestry for matching. The biggest limitation is that as you get more generations into the past, the sections become so short that they can’t be accurately identified. Most genealogists don’t think you can look back more than seven generations using this approach. At this point, you have 128 ancestors and the segments are less than 1% of their original size. Your 128 seventh generation ancestors normally produce more than a thousand potential cousins.

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FTDNA Estimates

When you take the AT-DNA test, you will get a list of these thousand or more potential cousins. An example of a small part of my results is shown below. FTDNA estimates the relationship range for each person and shows the amount of DNA that you share. The amount of DNA is listed using units of centiMorgans (cM). My top match at 366 cM matches over 1/3 of my DNA and is my 2nd cousin on my mother’s side. The fifth match is only 46 cM and is a much more distant cousin who I have not yet been able to link to my family tree. In most cases, matches less than 5 cM are not worth pursuing because they are mostly random noise. At that point you are eight generations or more in the past. Ancestry provides similar information for their Family Finder test but does not give the actual length of the matches.

FTDNA offers another interesting tool for examining your AT-DNA, the Chromosome Browser. This lets you see a graphic picture that shows the matching segments comparing you with people you select from your list of matches for comparison.

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Chromosone Browser Result

This is the chromosome browser result for me when compared with my 2nd cousin and two other people of unknown relationship. Each person’s matching segments are shown in different colors. The orange bars are for my second cousin. The green and blue regions circled are two distant cousins. The most valuable feature of the chromosome browser is that you can see if two of your matches share the same segment with you indicating you all have a common ancestor. In this case, the green and blue segments are not in the same positions as the orange, so I would look at different surnames for them. If two or more people match at the same place on a chromosome, then you can look for a single common ancestor to all of you.

FTNDA also has an independent site, GEDmatch.com that you can join and compare DNA data. This gives you access to people who are not on the FTDNA site. It also provides a collection of tools for searching and comparing DNA. I recommend that all FTDNA and Ancestry users load their data on GEDmatch as well. The tools available are not as slick as those at Ancestry and FTDNA, but you can get much more detailed results from GEDmatch than from Ancestry.

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Ancestry.Com Match

The Ancestry match for my second cousin is shown here. Ancestry correctly predicts the relationship in this case, but does not give any information about the amount of DNA we share. Ancestry does provide direct access to family tree information that is public and even connects groups of related people in DNA Circles. This particular circle has 13 members. With Ancestry, you don’t get member emails as you do with FTNDA and must communicate through the Ancestry message system. This means they won’t get your message until they log into Ancestry.com.

A few final cautionary notes about the autosomal test. If you have this test, you can expect to get about 1000 cousins to work through. I recommend that you make a list of all surnames in your family tree before you even start. You will need this and your matches will expect you to have it. Your matches are all the children of the 128 ancestors from seven generations back and more from earlier generations. If you do this test, you should expect to need to do some work to sort it all out. Using the chromosome browser can allow you to connect people up in useful ways, but can be a challenging task. Your success also depends on the genealogical information you and your matches have. One of the great frustrations is when you have a match to someone who has not entered a list of their ancestral surnames or does not respond to emails requests for information. In many cases people don’t know all their names back more than four generations, particularly on the maternal side.

In spite of the limitations, autosomal DNA can be very helpful. We often recommend it to people who don’t have a male Henderson for y-DNA testing. A solid autosomal match to someone in a Y-DNA family group can confirm membership in a family group.  People who get serious about autosomal testing often test with all three labs because each has a different database of roughly a million people. Unfortunately for me, Genetic Genealogy: The Basics and Beyond Kindle Edition by Emily D. Aulicinoneither FTDNA nor Ancestry have produced any close Henderson autosomal matches.

There are a variety of resources available to help you if you decide to take the plunge into DNA. The most comprehensive is isogg.org, the official site of the International Society of Genetic Genealogy. It has a beginner guide that is quite comprehensive. There are also books available to help you. One inexpensive guide is Genetic Genealogy: The Basics and Beyond Kindle Edition by Emily D. Aulicino.

 

 

 

 

 

 

Points of Contact

To learn more about the Clan Henderson DNA Project contact the DNA Project Administrator:

David Henderson

To get personal assistance with DNA or Genealogy related issues, contact the Clan Henderson Society DNA and Genealogy Coordinator. She can answer simple questions and suggest one of over 30 volunteers who might provide assistance. Note: this is a free service, managed by volunteers. First, priority is given to members of the Society. Second, we ask that you have patience--we are not a "for profit" company.

Tracy Rowan DNA and Genealogy Coordinator