Research Tip – Genetic Genealogy and DNA Testing
Over the past years, more and more genealogists have been exploring their genetic genealogy by having their DNA tested.
WHY BOTHER? WHAT WILL A DNA TEST REVEAL ABOUT MY GENEALOGY?
Before exploring genetic genealogy and DNA testing, it is worthwhile to discuss what all the fuss is about. There are really two answers to the question, “Why bother?”
- To learn about your paternal or maternal “deep ancestry.” This means that you will learn about the journey that your ancient ancestors (e.g., 50,000 years ago) made as mankind left Africa and spread out across the world. The answer to this question can be found by having a 12-marker test performed.
- To learn about more recent ancestors (e.g., within the past 8–12 generations) and to discover possible “genetic cousins.” By expanding from the introductory 12-marker test into more thorough DNA tests, you can identify your relationship to previously studied groups of people. By signing a release form to make your data available to match with others, you may be introduced to others who have had their DNA tested who may share a common ancestry with you.
Most testing services also sponsor surname studies, a way in which participants with a common shared surname can coordinate and compare their results with others in the surname group. These studies also may offer DNA testing services at “group rates,” thereby reducing your costs for the test(s).
THE BASICS: BOYS AND GIRLS
Each of us has two biological parents, and we inherit traits from each of them. In addition to our brown eyes or curly hair, however, we also inherit an amazing array of genetic information from each of our parents.
One of the characteristics that we are born with is our gender: male or female. A single pair of inherited chromosomes determines our gender. These sex chromosomes are called X and Y, and we get one from each parent. If we receive an X from our mother and a Y from our father we are a boy. If we receive one X from our mother and another X from our father we are a girl. This simple fact forms the basis for all of genetic genealogy.
Of importance to genetic genealogy is the study of two specific components of human DNA: that of the Y-chromosome for men, and of mitochondrial DNA (mtDNA) for women. The Y-chromosome is passed from father to son and mtDNA from mother to her children of both sexes.
MUTATION: THE BASIS FOR DIVERSITY
If everything in the world was always perfect, each strand of DNA would always replicate itself exactly. But reality, as we know, is often not perfect. So sometimes a change occurs. When this happens, a mutation in the DNA strand results. Sometimes these mutations are harmful and don’t last. But sometimes, they can result in beneficial new traits and will be incorporated into the population. These successful mutations result in the process called natural selection, made famous by Charles Darwin.
THE DIVERSITY OF HUMAN ANCESTRY
The fossil record and genetic evidence indicate that all humans today are descended from ancestors who lived in Africa about 150,000 years ago. About 60,000 years ago as the African climate changed, tribes began migrating out of Africa, following the better weather and the animals that they hunted.
Over vast stretches of time, different tribes followed differing migration paths, and eventually populated different parts of the world. And, over time, through genetic mutation (evolution) each tribe developed its own characteristic DNA variation.
Genetic scientists who have studied the DNA of the world’s civilizations have identified 23 unique sets of human DNA. Each DNA set has been assigned a letter (or pair of letters) from A through R. These groupings are the results of those genetic mutations in the indigenous African tribes as they scattered across the globe.
In recent years, several testing laboratories have been established in the United States and other countries to perform DNA tests for the express purpose of identifying ancestral origins for genealogical purposes. You may request a test kit from any of these firms.
It must be pointed out that these DNA tests are not designed to provide any medical information for the individual, nor do they provide information on possible genetic diseases.
Testing your Paternal Line
Men (only) have the option of testing their strict paternal line of descent: their father’s father’s father’s father’s father’s… father. This is because all men inherit genetic material from their father through the Y-chromosome. Some firms, therefore, call a paternal test the yDNA test.
Most genetic testing companies offer yDNA tests at several different levels. The following options are typical, listed in order of increasing cost:
- 12 marker test. This is the most basic test. The results of a 12 marker test will yield your “deep ancestry”—your paternal ancestry from about 10,000 years ago. This is done by studying the specific mutations in your DNA and comparing it to the DNA of known migration patterns of ancient tribes.
- 25 marker test. This is the “entry level” test for confirming a match to a known surname group.
- 37 marker test. This is similar to the 25-marker test, but the additional markers provide a better likelihood of matching to a surname group. Two persons with a 37-marker match shared a common ancestor “in recent times.”
- 67 marker test. This is the premier test (and the most expensive), for people who have a serious interest in detailing their genetic genealogy. It is a high resolution test, and two persons with a match share a common ancestor “in very recent times.”
Testing your Maternal Line
Both men and women have the option of testing their strict maternal line of descent: their mother’s mother’s mother’s mother’s mother’s… mother. All women inherit genetic material from their mother through mitochondrial DNA (mtDNA). Since men inherit through both the X- and Y-chromosomes, men can also test their maternal line. Men do not pass the mtDNA on to their children, however.
As with yDNA testing, mtDNA tests also come at differing levels, each with increasing cost:
- HVR1. Similar to the above 12-marker test, this test provides information on your deep ancestry (about 10,000 years ago).
- HVR1 + HVR2. This test can be used to determine if you and another person share a common maternal ancestor. Thus, it is frequently selected in doing maternal lineage studies. This test also verifies possible Native American and African ancestry.
- Full mtDNA Sequence. This is the most complete test. As the name implies, it tests your entire mtDNA sequence.
To gain further insight into the world of genetic genealogy, the Society has prepared a booklet entitled Genetic Genealogy and DNA Testing. This booklet is available for purchase from the Society, or it is free to members and a PDF file.
For further information, you may also wish to read any of the following resources:
Devine, Donn. Sorting Relationships among Families with the Same Surname: An Irish American DNA Study. National Genealogical Society Quarterly, vol. 93 (December 2005): 283–293.
Fitzpatrick, Colleen, and Andrew Yeiser. DNA & Genealogy. Hoboken, New Jersey: Rice Book Press, 2005.
Leary, Helen F. M. Sally Heming’s Children: Genealogical Analysis of the Evidence. National Genealogical Society Quarterly, vol. 89 (September 2001): 165–207.
Shawker, Thomas H., M.D. Unlocking your Genetic History: A Step-by-Step Guide to Discovering your Family’s Medical and Genetic Heritage. Nashville, Tennessee: Rutledge Hill Press, 2004.
Smolenyak, Megan, and Ann Turner. Tracing your Roots with DNA: Using Genetic Tests to Explore your Family Tree. Emmaus, Pennsylvania: Rodale Books, 2004.
Last modified: 23-Nov-2019 12:49