How to use your consumer DNA test results to solve your family history mysteries
by Jennifer MacArthur, Ph.D. and Robin Wirthlin
More and more people are taking DNA tests, either for fun—to see their predicted ancestral origins or ethnicity—or to learn more about their family history. DNA, which is short for deoxyribonucleic acid, is the genetic code carried in each of the cells in our bodies. It has always been with us and has been passed down from our ancestors throughout the millennia. DNA alone does not tell you a lot about your family history. But when it is used in conjunction with time-honored, traditional genealogical research, you have a powerful tool that will help you find your ancestors.
Most direct-to-consumer DNA tests don’t read your whole genetic code. Instead, they focus on tens of thousands of specific points – or markers – in your DNA that commonly vary from person to person. Companies such as AncestryDNA, FamilyTreeDNA, MyHeritage, 23andMe, LivingDNA, and others compare your DNA information with DNA information from other people in their databases. You are given a list of people with whom you share varying amounts of DNA. This “DNA match list” gives you a number in centimorgans (cM) or a percentage of the amount of DNA that you share with each person in your list. In general, the greater the amount of shared DNA, the closer the relationship.
There are three main kinds of consumer DNA tests which offer different sorts of genetic information:
Chromosomes are packages of DNA. Humans have 23 pairs of chromosomes, including the X and Y sex chromosomes. Autosomal DNA refers to the other 22 chromosome pairs. Autosomal DNA (atDNA) tests are best if you are interested in learning more about your family members, ancestors, or your ethnicity. They may be used to determine family relationships for about 6–8 generations. Beyond that, the amount of atDNA that is inherited from a specific ancestor may be too small to make a definitive identification.
If you are interested in learning more about your paternal line (the line that goes from father to father to father) take a Y-DNA test, or have a male in your family take one. The Y-chromosome is passed down father to son, unchanged for thousands of generations. A Y-DNA test will name a Y-DNA Haplogroup and give a list of people who share the same or similar genetic markers. Test as many markers on the Y-chromosome as you can afford. The more markers, the higher the resolution the test will be, and the matches you receive will be closer in a genealogical timeframe.
A mitochondrial DNA test provides information about your maternal line (the line that goes from mother to mother to mother). Mitochondrial DNA (mtDNA) is found in mitochondria, which are like battery packs for your cells—including egg cells. So mtDNA is passed down only from mothers to their children. Testing a direct female descendant can identify a mtDNA Haplogroup, and help you determine common female ancestors.
Using DNA Evidence for Family History Research
DNA evidence can prove or disprove close biological relationships in a family. There is a predictable average amount of DNA that is passed down from parents to children to grandchildren. Similarly, cousins, aunts, uncles, half-siblings, and other relationships have predictable ranges of shared DNA with a relative. Still, there is not enough information in the amount of DNA shared to determine the exact relationship without looking at known family trees and family history.
With access to DNA results and information about matching relatives, you can discover more family connections. For example, DNA evidence can help to separate and detect the unique identity of similarly named people. Many DNA testing companies now offer tools to more easily combine family trees and historical records with DNA information. Adding your DNA results to multiple databases increases your chance to connect with a long lost cousin who knows more about your common ancestors than you do, which may be the key to unlocking more of your family history mysteries!
A very important consideration in taking DNA tests yourself, and in encouraging friends and family members to test, is to contemplate the long-term implications of genetic testing. There is a possibility of uncovering unknown information, such as previously unknown relatives, or learning that some family connections are not biological. The tester needs to know about these possibilities before agreeing to take a DNA test, and if you will be overseeing the test results, they need to sign an informed consent agreement. This will help you and your family members be aware of the potential outcomes, both positive and negative, of DNA testing. Also consider the security of your genetic data by carefully reviewing privacy policies of the databases you join.
Ready to dive in to genetic genealogy? Read Robin’s blog series to get specific guidance on how to understand, organize, and evaluate your DNA matches.
Robin Wirthlin has a B.S. in Molecular Biology from BYU and a Certificate in Genealogical Research from Boston University. Robin is a professional genealogist who loves to use genetic genealogy to solve family history mysteries and break through “brick walls.”
Jennifer MacArthur, Ph.D. wants everyone to understand about DNA and genetics. As a freelance marketing writer, Jenn helps life science companies translate complex concepts into clear and compelling stories. Check out more at www.jmacphd.com.