The Simple Way to Understand Genetic Genealogy Tests, Part 1

As a co-administrator of a y-DNA/surname project, I and my colleagues get many questions about what various genetic tests can do for people. The long answer probably requires an advanced degree in genetics… something most participants don’t have. Here is a simpler explanation which is true in the macro sense, though extended details are not covered.


Basically, there are three different kinds of genetic tests used in genealogy. One test is for markers on the y-chromosome. This test requires a sample from a male, as females do not have a y-chromosome. It looks at markers and allows you to compare them with other samples of known or unknown genealogies in hope that you will find a relative who proves a specific lineage.

The second type of test concerns mitochondrial DNA, the DNA which was in the egg from your mother (that became you!) and consequently the bodies of your cells today. Mitochondrial DNA comes only from your mother. It is only passed down a female line. Your mitochondrial DNA came from your mother and her mother and her mother back in time to the first human woman.


The third test is of autosomal DNA. Autosomal DNA is the DNA other than the sex chromosomes. In reproduction the autosomal DNA is mixed up with the creation of each new child, sometimes coyly referred to as a “transmission event.”

These three types of tests give us different information; and importantly, that information yields different genealogical information for different time periods.

Let us begin with our mothers and mitochondrial DNA. Mitochondrial DNA changes very slowly. One research paper recently reported a rate of one change per 371 “transmission events.” Thus, over 371 generations, there is a 50% chance that one child will have a change in her/his mitochondrial DNA. Population geneticists and genealogists define a generation as somewhere between 20 and 30 years. If we use 25 years here, we are talking about the likelihood of one change per 9,275 years. Now this change is random, so it could have occurred between you and your mother, but the likelihood of that is 1/371.

Here’s the simple way to look at this. Suppose we represent your mother’s mitochondrial DNA (mt-DNA) as a hand of four playing cards: the 2 ♦, the Queen ♥, the 10 ♠, and the Knight of ♣. The odds are that your mt-DNA is exactly the same (the 2 ♦, the Queen ♥, the 10 ♠, and the Knight of ♣); actually 370/371, or 99.73%. And if there is a change, it is minor and closely related. An example of a change would be represented by this configuration: the 2 ♦, the Queen ♥, the 9 ♠, and the Knight of ♣. We expect this same situation to hold true up and down your maternal line. A fifth cousin sharing the same maternal lineage will likely have the exact same mt-DNA with perhaps one minor change. For that reason, mt-DNA is very useful for establishing maternal shared ancestors, but of much less use to understand lineages in what we call genealogical time—the seven hundred years since surnames and some record keeping became more common. (Though royal lineages have been kept for thousands of years.)

Because mt-DNA changes so slowly, and because it is present in much larger quantities in people than other DNA and usually survives for years after death and burial, it is used to understand the genetics of earlier humans. One group of people killed by the Mount Vesuvius volcanic eruption of 24 August 79 AD (which destroyed the two ancient Roman cities of Pompeii and Herculaneum) was analyzed over 1,600 years later. The mt-DNA showed that six of 13 individuals in one house were maternally related, all having the unusual haplogroup T2b. Because of the slow rate of change of mt-DNA, scientists can confidently say that all of our mitochondrial lineages trace back to a common ancestor who lived in Africa 100,000 to 150,000 years ago. Some lineages migrated out of Africa about 60,000 years ago, while others remained.

I will return with further information about the rates of change for y-DNA and the autosomal DNA. The card game becomes much more complicated! Mitochondrial DNA changes so slowly you could think about dealing out the same four cards 371 times in a row. But for y-DNA (at 67 markers) it is just 3-4 hands in a row. And for autosomal DNA you get a new shuffle and a new hand with every transmission event.

Lalia Wilson for the Taylor surname project

Collaboration is the Name of the Game

A lot of work goes on behind the scenes of this Taylor DNA project. Among what happens is that the administrators are actively working with project members to facilitate a win-win experience for all. One of the principal parts to making your experience with the project a success is offering as much information as you can about your family lines—excluding personal information on living persons.

 

On your personal page at www.familytreedna.com, you have ways to input data about your father’s line, your mother’s line and all family lines. These can be input as a gedcom or individually.

When you post this information, it allows near-matches to begin to see where their line connects with your line. For best results, all project members should be forthcoming with family pedigrees.

But your job is not over! A next part is to actively collaborate with people who ask you for information. This means responding in a timely manner to project members who inquire about possible connections. It means responding thoughtfully. It means being responsible for your own safety and protection as well—don’t share mother’s maiden names or birthdates or social security numbers for living people!

It may be that you get a lot of e-mail; I do. If you are busy, give a quick response. “I got your message. I may have some information on your question. I cannot get to it until after the 20th. Please contact me again if I don’t get back to you.”

 

I have been in many conversations with project members and other genetic genealogists about how to best work collaboratively. Here are some thoughts from our member Richard A. Taylor:

 

I don't understand why so many folks spend all their money and time testing with FTDNA or some other DNA testing company, joining the Family Finder group and/or signing up for any of the many groups, projects or blogs and then DO NOT SUBMIT FAMILY TREES, GEDCOMS, MULTIPLE SURNAMES OR NOTES ABOUT THEIR FAMILY ORIGINS AND WORST OF ALL - DO NOT REPLY TO A CONTACT E-MAIL MESSAGE OFFERING TO SHARE/COMPARE INFORMATION!!!

 

I've sent out e-mails to three people listed as possible matches, 2 for my line and 1 for a friend’s Taylor line, without any reply or acknowledgement. Reckon this is sort of analogous to "leading a horse to water but you can't make him drink."

 

Why go to all this trouble if you're not going to respond or share any info?

I know that Dick’s a bit annoyed in his tone above, but he is simply repeating some of the frustration that all of us face as we start working through our matches in the Taylor project (and with our other related lines).

 

To the extent we can, we should work to make our own experience and that of our related lines as pleasant as possible. We can do this by submitted your family pedigree, or gedcom.

• Did you post your earliest known ancestor (of your male Taylor line)?
• Have you posted your earliest know female ancestor on your female-to-female line?
• Finally, if you are doing the Family Finder test, have you posted all the known surnames for all your lines in the last seven generations?

By completing these details, which are about people who are usually many years deceased, you improve your chances of determining how you link to anyone whose DNA you match. You also improve the ability of those you match to find their link with you. (This is because the person you match may have more family information than you have, which is a blessing in that it adds important family information you may not have known about.)

 

Lalia

  

Always happy to share Taylor or any other info I possess. My wife (surname Ford/Foard from MD to NC to TN to VA) and I have been researching since about 30 years or more.

 

 Richard (Dick) A. Taylor

 

 

 

 

 

Newly Available Technique at FTDNA

Greetings,

Family Tree DNA has announced to current members that they can do autosomal testing of their DNA. This new test is called Family Finder by FTDNA. So here's a quick explanation of what that means. If you are a member of a surname project, such as the Taylor project, you have had y-DNA tested. This is the Y-Chromosome which is inherited from father to son throughout history. The minor changes that occur in that chromosome happen such that over generations family lines separate. Y-DNA is extremely useful to determine one's patrilineal lineage.

Similarly mt-DNA is testing the genetic material that comes only from one's mother. She got it from her mother and so on back in history. Mitochondrial DNA mutates more slowly than y-DNA, making it less useful in following one's ancestors in historical time, but more useful, perhaps, for deep ancestral investigation.

Autosomal DNA is the DNA in the 22 chromosomes that do not include the final 23rd chromosome that determines whether we are male or female. Thus the remaining 22 chromosomes have genetic pieces from all our ancestors, not limited to our father's direct paternal line or our mother's direct maternal line.

Family Tree DNA proposes to test your sample, should you request the test, and compare it with their database of samples. They assert that with this test you can locate genetic relatives in the database from as far removed as 5th cousins. This would include relatives unknown to you, who may have been lost to your version of your combined family history. While the new autosomal testing will be administered separately from the surname project to which you belong, it will provide useful information that may enhance your knowledge of your family tree. See the quote below from the FTDNA website:

"Surname projects can use Family Finder to better define branches in a family tree. By using Family Finder testing, close Y-chromosome and mt-DNA matches without traditional records may be assigned to a pedigree with greater confidence. Even more exciting, surname projects may now bring female cousins into the project as additional evidence."

Lalia Wilson for the Taylor Surname Project