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DNA Tests and Terms: A Genetic Genealogy Glossary

By Blaine T. Bettinger Premium

Genetic genealogy and DNA testing is a 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.

The ABCs of DNA and Genetic Genealogy

Autosomal DNA (atDNA, admixture DNA)
Centimorgan
Chromosome
DNA Testing Companies
Genome
DYS
Genetic Cousins
Haplogroup
Haplotype
Mitochondrial DNA (mtDNA)

Modal
MRCA
Mutation
NPE
Recombination
SNP
STR
Taking a DNA Test
TMRCA
Y-DNA

Autosomal DNA (also called atDNA or admixture DNA)

Genetic material inherited equally from mother and father. It’s genealogically useful for ancestry back through about five to seven generations. Beyond that, you may not have inherited enough DNA from any one ancestor for that person to be represented in your 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. 

Details about atDNA

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.   

Centimorgan (cM)

A measurement of the distance between genetic markers on the DNA based on the expected frequency of recombination with each generation. On average, one cM equals one million base pairs. In general, the more centimorgans you share with a genetic match, the closer your relationship (although individuals related through multiple ancestors also may share a high number of centimorgans).

Chromosome

A threadlike strand of DNA that carries genes and transmits hereditary information.

DNA Testing Companies

Written by Susan Wenner Jackson and Diane Haddad

23andMe

Here, you can purchase an autosomal test that provides only results about health risks and inherited traits, or that plus ancestry information. 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.

AncestryDNA

This well-known service, run by Ancestry.com, 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 Ancestry.com, 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).

Family Tree DNA

This company offers the broadest array of tests, including an the Family Finder autosomal test 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 or mtDNA tests 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.

MyHeritage DNA

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.

Oxford Ancestors

This British company can analyze your mtDNA or Y-DNA for ancient origins. Results are geographical only, and don’t include matches.

Genome

All the genetic material in the chromosome set of an organism. 46 chromosomes make up the human genome.

Genotype

The genetic makeup of a particular individual.

DYS (DNA Y-chromosome Segment)

DYS followed by a number identifies a short segment of Y-chromosome DNA, also called a Short Tandem Repeat (STR) or a marker. A Y-DNA test reveals how many repeats of a particular nucleotide sequence are found at that DYS marker. For example, DYS390 is one of the most commonly tested Y-DNA markers, and values for the marker typically range from 19 to 28 repeats.

Genetic Cousins

Individuals whose DNA test results match one another. You may have cousins who aren’t genetic cousins—that is, you and your cousin don’t match on DNA tests because you didn’t inherit enough of the same DNA from the same ancestor.

Haplogroup

A collection of related haplotypes with a common ancestor. The haplogroup (also called a clade) is usually defined by a single nucleotide polymorphism (SNP) mutation that arose in an ancestor hundreds or thousands of years ago, and is found in all of the descendant haplotypes.

Haplotype

An individual’s set of single nucleotide polymorphisms (SNPs) or DYS markers. Males who are recently related through their paternal line will have similar haplotypes and belong to the same haplogroup. The more diverse two haplotypes are, the more time has passed since their most recent common ancestor.

Mitochondrial DNA (mtDNA)

Genetic material both males and females inherit from their mothers. Because it’s passed down mostly unchanged from mothers to daughters, mtDNA can tell you about your maternal line—but because this type of DNA mutates infrequently, the results reveal only “deep ancestry,” not definitive links to recent generations. So while MtDNA can show whether two people (men or women) are related through their maternal line, it can’t tell you whether they’re second cousins or 20th cousins.

The set of most-common DYS values in a group of closely related haplotypes. A particular branch of a surname, for example, might have a slightly different modal from another branch of the name.

MRCA (Most Recent Common Ancestor)

The most recent paternal ancestor of two males. Every male on earth shares an MRCA with every other male, although some will have an MRCA thousands of years ago and others will have an MRCA within the last few generations. Y-DNA results can reveal how many generations have passed between two participants and their MRCA.

Mutation

A usually harmless change in the DNA sequence. A mutation can change the value of a DYS marker, for example. Although mutations are random, they typically occur at a known rate and thus provide a rough molecular “clock” useful for surname studies.

NPE (Non-Paternal Event)

A break in the Y-chromosome line resulting from adoption, infidelity or another cause. NPEs (also known as non-paternity events or false paternity) can be detected by DNA testing.

Recombination

The exchange of DNA segments at conception. Due to recombination, you inherit less autosomal DNA from each generation going back in time.

SNP (Single Nucleotide Polymorphism)

The mutation of a single nucleotide in the Y-DNA sequence. One of the nucleotides, represented by the letters A, T, C or G, replaces another at that location in the sequence. Haplogroups are defined by SNPs.

STR (Short Tandem Repeat)

A repeat of a short nucleotide sequence on the Y-chromosome. The DYS390 marker, for example, is an STR with between 19 and 28 repeats of the short nucleotide sequence. Closely related males will have a similar number of repeats.

Taking a DNA Test

Written by Susan Wenner Jackson and Diane Haddad

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.

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.

TMRCA (Time to Most Recent Common Ancestor)

An estimate of the amount of time between two males and their most recent paternal ancestor, calculated using differences between the two haplotypes.

Y-DNA

Genetic material passed down from father to son. Because surnames also pass from father to son, Y-DNA tests can confirm (or disprove) genealogical links through a paternal line.

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.

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