DNA and Family Genealogy

Posted on June 1, 2016 by bob in Discover Your Past, DiscoverYou, Features

“There are three different types of genetic tests that can provide genealogical insight,

each of which has its own use.”

by Alan Wallace

Along with its uses in medicine and forensics, DNA tests can be useful in solving genealogical puzzles.

You might be interested in DNA testing if documentary evidence is lacking or inconclusive, leaving you facing a “brick wall” about the identity of a particular ancestor. If DNA testing shows that you share a common ancestor with someone who has better data, you may be able to resolve your genealogical enigma.

To choose a DNA test and provider, it is important to understand some basics of DNA. Otherwise, you can pay for information that may not help you. Broadly speaking there are three different types of genetic tests that can provide genealogical insight, each of which has its own use.

Mitochondrial DNA (mtDNA) is tested to identify or confirm that two females share a matrilineal ancestor. Since mutations of mtDNA occur infrequently, the mtDNA of a woman living today will typically be identical or almost identical to that of her mother, her mother’s mother, and so on for many generations. By extension, the mtDNA of all women living today who are directly descended through maternal lines from a common ancestor within the past several hundred years will have relatively few variations.

Y DNA is tested to identify or confirm that two or more males share a patrilineal ancestor. Like mitochondrial DNA, mutations of Y DNA occur infrequently. The Y DNA of a living male will closely resemble that of his father and his father’s paternal ancestors. Therefore, the Y DNA of  men living today who are directly descended through paternal lines from a common ancestor within the past several hundred years will show relatively few variations.

Autosomal DNA tests examine segments of genetic material that are not gender specific. They can identify family connections originating within 5 generations of the subject providing the test sample. DNA matches from autosomal tests will not provide clues as to whether the common ancestor was male or female or how many generations ago the common ancestor lived.

To take things a step farther with Y DNA testing, it can use either of two approaches. The first looks at segments of Y DNA for short tandem repeats (STRs). Tests of this type usually examine 30-120 STR markers. The presence of more matches suggests a closer relationship or nearer common ancestor. The other type looks at single nucleotide polymorphisms (SNPs). This approach usually provides higher resolution than STR testing.

If you want a better grasp of the subject before having DNA testing done, you can spend some time at www.ISOGG.org (International Society of Genetic Genealogy). This is a reliable and objective information source. Among the terms you should be familiar with are MRCA (most recent common ancestor), haplogroups (people who share a common ancestor), subclades (subsets of haplogroups), haplotypes (group of genes inherited from a common ancestor), chromosomes, alleles, biogeography, etc.

Presently there are three primary providers of genealogical DNA testing: 

Ancestry DNA, www.dna.ancestry.com

Family Tree DNA, www.familytreedna.com

23andme, www.23andme.com

In choosing a provider, here are some items that you may want to consider:

1. What tests does the provider offer?

2. How many people are in the provider’s database against whom your data will be compared?

3. What matching information will the provider supply?

4. What is the cost of the test(s) in which you are interested?

According to ISOGG.com, AncestryDNA presently offers only autosomal testing. 23andme seems more focused on health and science research than on genealogical applications. Family Tree DNA offers autosomal, mitochondrial and an array of Y DNA tests. It also is reported to have the largest customer database against which the results of new tests can be readily matched. In addition, they host most of the DNA surname projects, helping connect people who share a last name and similar DNA.

In the interest of full disclosure, I had my first Y DNA test performed by Family Tree DNA several years ago and have upgraded to more rigorous tests more than once since then to obtain greater specificity. My motivation has been an effort to solve the conundrum of my male ancestry prior to 1813. The testing process itself is simple and painless.

The test provider sends a kit. The subject collects and returns a sample of genetic material (often a cotton swab rubbed on the inside of the cheek). Testing takes several weeks. Family Tree DNA sends an email when new results post on their site, which also provides access to information about matches to others in their database. Each time a new customer’s DNA matches that of an existing subject, the existing subject gets an email alert.

To extend one’s search for matches, a subject who has received test results from any provider can manually enter his/her specific results in the database of other providers, sometimes at a modest cost, at www.ysearch.org (for Y DNA) and at www.gedmatch.com.

If you are a female needing a Y DNA test, get a sample from your father, a brother, uncle, nephew or male first cousin who is connected through a continuous male line to the male ancestor(s) in whom you are interested. If you are male needing mtDNA results, get a female relative directly descended through a continuous line of females to the female ancestor(s) you are researching. Y DNA and mtDNA tests cannot cross genders at any point in the ancestral line.

Finally, keep in mind that genealogical DNA testing is fairly new. Right now the databases contain no more than a few million results at most. However, the number of results will no doubt continue increasing, lifting the odds of getting useful matches. In addition, getting test results into the system while a willing relative is alive to provide the DNA sample could avoid the frustration of having no direct male descendant to test for Y DNA or direct female descendant to test for mitochondrial DNA.

Alan Wallace also writes the monthly MoneyWise column in Prime magazine.

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