Autosomal DNA Tutorial

Several people have told me or written to me that they are not understanding this DNA and genealogy.  Here is some of what I have learned since testing my DNA at 23andMe.com.  I continue to learn by reading about genetics and by manipulating the data at 23andMe as well as Gedmatch.  I hope this is understandable without sounding like a biology lecture.

DNA is your genetic material.  Parents pass about half their DNA to each child.  Scientifically tracing a person’s DNA can assist a genealogist in identifying ancestors and descendants of those ancestors.  Submitting your DNA will not produce a family tree.  You still need to continue researching paper records (or digitized images) and visiting cemeteries.  The DNA results that I am presenting from 23andMe are autosomal tests.  This means that the genetic material was inherited from both parents, which in turn was inherited from both of their parents (your grandparents), and so forth.  You likely carry at least a little bit of DNA of all of your ancestors who lived centuries ago.  Some of their descendants, your distant cousins, also carry the same little bit of DNA.  Autosomal DNA testing looks for identical areas of DNA between two people.  When identical pieces are found, the two of you are matched up as genetic cousins.  You then can work together, analyzing your family trees, to discover which ancestor or ancestors you have in common.  Below is the best diagram I have uncovered that illustrates how an individual alive today has DNA comprised of ancestors from a few generations ago.

Based on how much DNA you share with another cousin, a prediction can be made on how close a relationship the two of you have.

Keeping in mind the above factors, take a look at a typical match of my father.

23andMe.com

My father shares 0.10% (that is a tenth of a percent, not ten percent) of his DNA with A. J.  The identical area is on chromosome 15 on one segment covering 7.0 centimorgans (cM).  Using the percentages above, 0.10% puts them between fourth and fifth cousins.  A fourth cousin or more distant would share 5-50 cM.  A third cousin once removed or more distant would share just one segment.  How is A.J. related?  We have no idea.  But that is a typical match for my father.  If they are fourth cousins, they share a pair of great great great grandparents.  To evaluated how possible it could be to identify how A. J. is related, I see how many of my father's 32 great great great grandparents I can identify.  19.  I can name 19 of the 32.  A. J. sees nothing in common with her tree, though she cannot identify all of her 32 either.  That leaves a lot of room for missing the common ancestor.  [I can identify all 16 of my father's great great grandparents.  Four were born in Germany; eight were born in New Jersey; and four were born in New York.  Knowing locations is also very important for noticing links.]

My father’s known third cousin also submitted his DNA.  Here is what their comparison looks like.

They match 0.93%, which is consistent for third cousins.  The cM total is 69.5 and within the 43-150 cM range for third cousins.  The match is on two segments, which is consistent with a third or more distant cousin.  Their DNA comparison is exactly on target for their relationship as supported by documentation.  They share a pair of great great parents.  We do not know, though, if the DNA shown above matches great great grandpa Calvin Cook or great great grandma Mary Neal.

Next compare a typical match for my mother.

A. L. and my mother share 0.34% of their DNA.  This would make them between third and fourth cousins.  They match on four segments, which is consistent with a second cousin once removed through a third cousin once removed.  Yet A. L. is predicted to be a DISTANT cousin.  Why?  Because of the total cM, which is 24.5 and more consistent with a fourth or more distant cousin.  Matching on several tiny segments is indicative of ancestors who intermarried.  A. L. was born in the United States, but wrote us that both sides of his family lived in the same little towns in Latvia and Ukraine for many generations and were Ashkenazi Jewish.  How is A. L. related?  We have no idea.  My mother currently has over 1300 genetic cousins in the system.  1100 of them match on two segments or more.  My father, for comparison, has 670 matches.  27 of them match on two segments; one matches on three segments; and I match him on 24 segments.

I hope that this tutorial helps you better understand my DNA presentations here.  Other than my father’s known third cousin and my mother’s brother, I have not discovered the connections to any of my genetic matches, but I am getting closer every day.  The more ancestors that you have identified, the greater your chances of success.

DNA matching: Half siblings

My DNA quests continue.  My mother's half brother was kind enough to submit his DNA specimen to 23andMe.com.  I am busy analyzing the results.  They share 26.6% of their DNA.  Full siblings share about 50%.  To interpret, each of them has about 75% of unshared DNA.  25% is from their mother, and 50% from their respective fathers.  If a genetic distant cousin matches one half sibling and not the other, we still do not know which parent holds the relation.  But if a genetic distant cousin matches both half siblings, then the relation is through their common parent.  Here is what my mother's comparison to her brother looks like.

23andMe.com
Autosomal DNA comparison of half-siblings (sister and brother sharing mother)

My uncle matches me 14.2%.  This is roughly half of the match between him and my mother.  This is because approximately half the DNA is lost from one generation to the next.

23andMe.com
Comparison between my mother, her half brother, and me.

This information is very valuable because anyone who matches both my mother and her brother matches on my maternal grandmother's side of the family.  The dark blue areas in the above graph are areas of my DNA that are identical to my maternal grandmother.  You can see how some segments break into tiny pieces quickly, while other stayed intact through a few generations.  The blank areas contain some more of my maternal grandmother's DNA along with my paternal grandfather's DNA.

The difficulty with identifying the common ancestor of genetic distant cousins is that you have two possible paths to follow at each generation as you travel back.  I know which parent to credit my matches to because both of them are in the database.  But beyond them, I do not know which of their parents share the relation, and so on.  At least now I have a better chance of identifying common ancestors by determining which ones match my maternal grandmother.  I will be explaining more and sharing examples in upcoming posts.

Roots into the Future, part two

Last year I received a free autosomal DNA testing kit from 23andMe.com through their Roots into the Future program.  According to their website, the purpose of the program is to increase understanding of the link between DNA and disease in African Americans.

The person who ended up using the kit was someone whose background I had researched in the past with little success.  She was raised in an orphanage in Genesee County, New York and had only the name of her mother.  The name was common, of course, and I was not lacking in finding thousands of women with the same exact name.  She submitted the kit in December and the results took about six weeks.

She was matched up with 44 other genetic relations.  This does not provide much to work with.  (For perspective, the other accounts that I manage have far more matches.  My mother and I have about 1300 each, while my father and his third cousin have around 600 each.)  The closest relation shares 0.50% over four segments.  This is outside the parameters for an accurate prediction of the closeness of the relation, but it can be characterized as distant.  The "Show Close Relatives" icon appeared and pressed it.  No other matches appeared.  I am not sure if this means that there are close relatives lurking in the database.  I initiated contact with all relations and just a few have responded.  They are related beyond a third cousin level, so we cannot map out this elusive family tree yet.

Autosomal DNA testing will reveal relatives and can be very useful in cases such as this when parentage is unknown.  But unless a very close relation surfaces and agrees to communicate, we will only have vague notions of possible ancestors.

Your identity is concealed from "close" relatives- first cousins and nearer.  Both parties must consent to be revealed.

23andMe.com provides an additional warning before you consent to view close relatives.
It is possible to discover that your parents were not biologically related to you,
or that a parent or aunt/uncle had children you were not aware of.