Monday, April 3, 2023

Genealogy: DNA Testing - Now What?

 DNA Test Results
Genealogy Research

There are several reasons for people to take a DNA test:
  • To learn more about their ancestry: 
  • To learn about their health risks: 
  • To find long-lost relatives. (DNA tests can be used to find relatives who share a common ancestor.) 

Background: What sparked this blog?

My son has expressed an interest in researching his genealogy. I have a family tree on Ancestry that has over 2,500 people. (Of course, I've shared that with him). 

But I haven't explored his mother's roots. She and I divorced over 40 years ago, and don't talk much. What entries I've made to my Ancestry tree are 3:00AM hits, also known to researchers as "bright shiny objects."

In March, Joel ordered a DNA test through Ancestry. For a penny more he received a 90-day subscription to Ancestry records!

This will give my son something to do while we wait the 6-8 weeks for his test results to come back.

DNA Test Results: Now what?

I bought my own DNA test several years ago because it was on sale. That was my only reason for the purchase!  When my own test results came back, I asked "Now what?"

I discovered the Pinellas Genealogy Society. It is a really strong organization, and I was eventually drafted as its technology director. We pivoted to virtual classes in 2020, and in 2022 we started hybrid classes.  I was the primary admin - which meant I sat through every class that's been taught in the last 4 years.

I've developed my own perspective for a newcomer's viewpoint. Here is how I would teach a beginner's DNA class:

Dear Son,

A single test is useless.

The results from a single test are pretty useless. It's just a boring string of letters. When you look at the raw results, the most you can do is nod your head wisely and say "OK."

DNA tests have value only when compared to other DNA tests. The stereotypical comparison is paternity. The father's test results by themselves are useless. The child's test results by themselves are useless. The value is in the comparison of those two tests.

Bottom line: you tested at Ancestry, and today Ancestry as over 20 million tests to compare your results to. You can upload your test results to other websites to access several million more. The more tests for comparisons, the better!

Ethnicity Estimates

One testing company had a memorable TV commercial where someone had to trade their lederhosen for a kilt based on ethnicity estimates. From my perspective, it was a bit misleading.

What I would like to do next is explain how ethnicity is only an estimate, and how it can change. It may even morph into something completely different over time.

Here's how.

Son, you live in Georgia now. The surrounding states are Florida, Alabama, Tennessee, and South Carolina. You've been told all your life that your roots are in Alabama.

In January, the company had 100 tests from each of the states. You matched 80% of the people from Tennessee. You also matched 10% of the people from Alabama. and 10% of the people from South Carolina. The company would tell you that your family is mostly from Tennessee.

By July, the company has completed another 900 tests for a total of 4,001 results. (You're the "1" in 4001.) This time your matches are different! You matched 50% of the people from Alabama. You also matched 40% of the people from Tennessee. and 10% of the people from South Carolina.

Hooray! You can change your colors from Orange to Crimson!

By December, the company has completed another 1,000 tests for a total of 8,001 results. (You're still the "1" in 8,001.) This time your matches are different! You matched 70% of the people from Alabama. You also matched 20% of the people from Tennessee. and 10% of the people from South Carolina.

Your test results did not change. Your family heritage did change from 80% Tennessee to 70% Alabama. How? The company just has a bigger number of tests to compare yours to. And, you did not match me because I didn't test with them.

Vocabulary Lesson:
MPH & cM (Centimorgans)

I'm going to pause for a brief vocabulary lesson.

A unit of measure for an airplane's speed is "miles per hour" (MPH). There are a lot of details involved in that (headwind, altitude, temperature) that advanced users will argue about. For practical purposes, MPH is "good enough." You can learn about the other nuances later.

The unit of measure for measuring shared DNA is "centimorgans" (cM). There are a lot of details involved in that (for example, snippets) that advanced users will argue about. For practical purposes, cM is "good enough." You can learn about the other nuances later.

You have 7,400 cM to Measure

It pains me to use round numbers and approximations because I have an engineering background.  I want to apologize for the liberties that I'm going to take in this section.

Don't ask me why DNA tests use 7,400 centimorgans as the starting place. The reason is probably buried deep in the details. Even though I use the even number 7,400 the actual number is probably closer to 7,500.

I found this on Google: "The length of a piece of DNA is measured in centimorgans. The total length of all your chromosomes combined is around 7400 cM. Since a person inherits half of their DNA from each parent, you share about 3700 cM with each parent. The exact number for each parent/child relationship can vary slightly, but not by a lot. - "

50% from each parent

You inherit about half of your 7,400 DNA from each of your parents. That's 3,700 from me, and 3,700 from your mother.

That 3,700 number also defines what you pass on to your children. That's half of their 7,400 cM. They get the other 3,700 from their mother.

About 3,700 cM defines a parent-child relationship

25% from each grandparent

I get half of my DNA from each of my parents.

Of the 3,700 cM I pass along to you, 1,850 cM comes from my mother and 1,850 cM comes from my father. 

About 1,850 cM defines a grandparent-child relationship.

12-1/2% from each great-grandparent

You get this picture.  You share about 925 cM with each of your great-grandparents.


Bottom Line:  cM matching starts at 3,700 and gets smaller the farther away you are from the other person who tested.

The actual numbers get even trickier.

Here is a chart that shows relationships and DNA cm numbers: 

Start with "Self" in the white block near the center. That's you. Your parent is in the next set of blocks above you. You can see that the relationship DNA cM measurement could be 
  • as low as 2,376 cM, and
  • as high as 3,720 cM, and
  • the expected range is about 3,485 cM.
Blaine Bettinger is considered one of the go-to people.

The Next Step

What do you do with that information? Here are two old videos links for your next step. Old? They were recorded in 2016, when Ancestry only had 2 million results instead of the 20 million they have now!
  • Video: AncestryDNA | You Received Your Results. Now What? Part 1 - this YouTube video shows you how to look up your enthnicity in Ancestry DNA results:
  • Fortunately, a lot of the drudgery is done by Ancestry. They will review their 20,000,000 test results, give you a list (most matches to smallest), then suggest possible relationships. Ancestry will even give you a way for you to contact them.
    (However, the matches don't have to respond.)
  • Video: AncestryDNA | You Received Your Results. Now What? Part 2 - This video teaches you how to translate your DNA matches:

Your First Step: DNA Test Results

At the beginning of this blog, I said there are three reasons why people take DNA tests.

DNA testing is another tool for Genealogy. It confirms research you've already done or suggests new people/places you can explore. is starting to look at other possible conclusions. They are suggesting and asking about traits. I don't think they're getting into inherited health risks.

Finally, I know about two adoptees on my side of the family. I don't know anything about their DNA research results.

It's a start: Enjoy the ride!

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