The Abcs of DNA

The Abcs of DNA

Genetic genealogy doesn't have to be scary. We'll spell out how to get started with DNA testing and what family history you can learn.

Many of us wonder how Irish or Italian we actually are, or whether we really have American Indian or German roots. You might ponder whether you’ll ever learn who Great-great-grandma’s mother was, whether your Schmidts or Joneses are related to the Schmidts or Joneses two towns over, or how many distant cousins are out there doing genealogy research. You might be adopted and looking for your birth family. 
Genetic genealogy and DNA testing is a new frontier is brimming with the potential for answers. By examining your genes, scientists can tell whether you share an ancestor with someone, about how long ago that common ancestor lived, and your ethnic origins.

How to do genetic genealogy and DNA testing

Before you begin exploring DNA testing, it’ll help to understand a few biological basics. There are three types of genetic data: autosomal, mitochondrial DNA and Y-DNA.

Autosomal DNA

If you’re new to genetic genealogy, autosomal DNA testing is probably what you’ve heard about. Ninety-nine percent of your DNA is autosomal. Both male and female children inherit autosomal DNA equally but randomly from both parents. Thus, siblings on average have 50 percent overlapping DNA (except for identical twins, whose DNA is 100 percent the same). First cousins have on average 25 percent overlapping DNA. 

Based on the amount of autosomal DNA you share with a match, test results can tell you approximately how far back your common ancestor lived and estimate your relationship. It’s up to you to determine who that ancestor might be, by studying your DNA match list, comparing your genealogy info with your matches’, and doing paper research.  
Autosomal tests aren’t helpful farther back than five or six generations, though, because at that point you don’t have enough DNA from any one ancestor for it to be reflected on your test.  

Autosomal tests also express your ancestry in terms of percentages from various ethnicities or geographic origins, such as Scandinavian, British, Eastern European, etc. This breakdown depends on what “reference populations” the testing company compares your results to, so you might get different results from different companies. It’s a developing but promising field: With more research, companies are improving ethnicity estimates and can even use results to predict ancestors’ migration paths.   

Mitochondrial DNA

Both males and females have mitochondrial DNA (mtDNA), which is inherited from the mother. Men don’t pass their mtDNA to their children. Since mtDNA mutates so infrequently over generations, it can reveal “deep ancestry,” or where on the globe your genetic origins lie. MtDNA also can show whether two people (men or women) are related through their maternal line—but it can’t tell you whether they’re second cousins or 20th cousins. 


A man inherits his Y chromosome from his father (women have two X and no Y chromosomes). This inheritance pattern means a Y-DNA test won’t show you whether Henry is your dad’s mother’s brother’s son, because your grandmother didn’t have a Y-chromosome to pass down to you.  

Y chromosomes mutate occasionally, allowing these tests to show more-recent relationships. The Y-DNA test can’t name an ancestor, but it can answer questions about whether you’re related to someone who shares your last name. Tests come in “resolutions” of 12 to 111 markers—the higher the resolution, the more precise the test. Testing 67 markers is sufficient for most genealogy researchers. Your Y-DNA results also can be used to estimate the geographic origins of your paternal line.

Even though she doesn’t have a Y chromosome, a women can benefit from a Y-DNA test by recruiting her father, brother or paternal cousins to take the test.


Taking a DNA test

Several companies offer various genetic testing services. Some offer information about both your genetic matches and your ancestors’ ethnic origins, and some offer only ethnic origins. If you’re interested in genealogy research, use a service that provides a list of matches—see 23andMe, Ancestry DNA, Family Tree DNA and MyHeritage DNA.

You’ll order a test kit containing a saliva collection tube or a cheek swab, follow the instructions to provide your sample and register on the company’s website, and send in your sample. Up to six weeks later (sometimes more, depending on the backlog of kits at the company’s lab), you’ll get an email to log in and view your results. 

Most companies provide anonymous DNA data for medical research. If you prefer to opt out, look for this option when you register your test. Read the testing service’s terms of service for more details. Prices below are regular, and here’s a secret: like these services on Facebook and join their mailing lists to find out about DNA test sales.

  • 23andme: Here, you can purchase an autosomal test that provides only results about health risks and inherited traits ($99), or that plus ancestry information ($199). The latter includes both ethnic origins and genetic matches. Matches’ family history information is limited compared to other sites, but can include ancestors’ names and places of origin. You also can send a message to a match through the site.
  • African Ancestry: This company specializes in telling you where in Africa your paternal or maternal line originated by comparing your Y-DNA or mt-DNA profile to the DNA profiles of reference populations in Africa. Results are geographical only, they don’t include a list of matching people. Tests run about $300.
  • Ancestry DNA: This well-known service, run by, offers only autosomal testing. You get a list of matches from the site’s pool of 4 million-plus DNA profiles, as well as ethnic results. You might be placed in a Genetic Community, defined by groundbreaking genetic research, of people with shared geographic ancestry whose ancestors followed characteristic migration patterns.

    If you also subscribe to, you can view family trees of matches who’ve linked trees to their profiles, and if you subscribe and have a public tree linked to your test, you can be placed in DNA Circles (groups of matches who have the same ancestor in their trees) and get New Ancestor Discoveries (suggests ancestors who might be yours based on groups you match). Tests cost $99.

  • Family Tree DNAThis company offers the broadest array of tests, including an the Family Finder autosomal test (about $89) that comes with advanced analysis tools such as a chromosome browser (which lets you see which segments of DNA you share with a match). It doesn’t have online trees, but you can view a GEDCOM file or family history information if your match provided it, and contact matches through the site.

    This is the only company offering Y-DNA (starting at $169) or mtDNA tests (about $200) that include matches in addition to geographic origins. Y-DNA testers can participate in surname studies. You can purchase packages of different tests, and provide a single sample. You also can transfer test results from other companies. 

  • Living DNA: This British testing company doesn’t offer genetic matches, but it does offer more detail on geographical origins within Britain than any other testing company can. It’s also launching a project to be able to do the same with German ancestry. It offers British origins information for autosomal, Y- and mtDNA. The test runs $159.
  • MyHeritage DNA: New to genetic genealogy testing, genealogy site MyHeritage offers autosomal tests with ethnicity estimates and a list of matches. Its collection of family trees from members around the globe may increase your pool of potential matches from your ancestral homeland. Its young database of DNA profiles relatively small, and analysis tools are still being built out. You can view a match’s family tree (if he posted one) and contact him through the site. You also can transfer test results from other companies. Tests run $99. 
  • National Geographic Genographic Project: This autosomal test provides only information on your family’s geographic origins; you won’t receive a list of matches or genealogically useful information. Results are used to study human populations and migration. The test costs about $150.
  • Oxford Ancestors: This British company can analyze your mtDNA or Y-DNA for ancient origins. Results are geographical only, and don’t include matches. Prices start about $250.

DNA testing tips

Despite the exciting potential of genetic genealogy, it’s not the Holy Grail of family history. Many now take a DNA test as their first research step, and some stop there. To answer your family history questions, though, you’ll also need to use traditional records and oral history.

Because of autosomal DNA’s random inheritance pattern, consider having other relatives test. Your siblings might match distant cousins you don’t match. Have older generations tested first: Your parents and grandparents and their siblings will have more of their ancestors’ DNA than you do.

When you view information about a match, pay attention to the amount of shared DNA, which can help you estimate how you’re related. Look at the person’s family history information, if any, for names and places in common with your research. See which other matches you share—someone who matches you and your dad’s brother comes from that side of the family.

If you’re considering a Y-DNA or mt-DNA test, have the right relative tested. Identify your genealogy question, then test someone who has the Y-DNA or mtDNA from that family line.

Genetic Genealogy Resources

Adapted from the print Family Tree Magazine


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