DNA tests are offered by a wide variety of testing companies, and each works a little differently. Most tests are sent with a cheek swab or small brush which you rub on the inside of your cheek, and then send back to the company in the provided sample container. Other companies may have you spit directly into a tube, or provide a special mouthwash that you swish and spit. Regardless of the collection method, however, what's important for the genealogist is which part of your DNA is being examined. DNA tests can help you learn about your paternal and maternal ancestry. There are also tests that can help you determine whether you are of African, Asian, European or Native American descent. Some of the newer genetic tests can also provide some insight into possible inherited traits and disease risk.
Y-DNA TestsUsed For: paternal lineage only
Available To: males only
Y-DNA tests specific markers on the Y-Chromosome of your DNA known as Short Tandem Repeat, or STR markers. Because females do not carry the Y-chromosome, the Y-DNA test can only be used by males.
The specific set of results from the tested STR markers determines your Y-DNA haplotype, a unique genetic code for your paternal ancestral line. Your haplotype will be the same as or extremely similar to all of the males who have come before you on your paternal line -- your father, grandfather, great-grandfather, etc. Therefore, once you have tested your Y-DNA STR markers, you can use your haplotype to verify whether two individuals are descendants from the same distant paternal ancestor, as well as potentially find connections to others who are linked to your paternal lineage. A common application of the Y-DNA test is the Surname Project, which brings together the results of many tested males with the same surname to help determine how (and if) they are related to each other.
Learn more: Y-DNA Testing for Genealogy
mtDNA TestsUsed For: Deep (distant) maternal lineage
Available To: females; males testing their mother's lineage
Mitochondrial DNA (mtDNA) is contained in the cytoplasm of the cell, rather than the nucleus, and is only passed by a mother to both male and female offspring without any mixing. This means that your mtDNA is the same as your mother's mtDNA, which is the same as her mother's mtDNA, and so on. mtDNA changes very slowly so it cannot be used to determine close relationships as well as it can determine general relatedness. If two people have an exact match in their mtDNA, then there is a very good chance they share a common maternal ancestor, but it can often be hard to determine if this is a recent ancestor or one who lived hundreds of years ago. You can also use an mtDNA test to learn more about your ethnic ancestry, or to trace your maternal lineage to one of the Seven Daughters of Eve, prehistoric women who shared a common maternal ancestor named Mitochondrial Eve.
A range of mtDNA tests are available that analyze different regions of the mtDNA sequence. It is important to keep in mind with this test that a male's mtDNA comes only from his mother and is not passed on to his offspring. For this reason, the mtDNA test is only useful to females, or for a male testing his mother's lineage.
Learn more: mtDNA Testing for Genealogy
Autosomal DNA TestsUsed For: Ethnic ancestry, plus relative connections on all branches of your family tree
Available To: males and females
Autosomal DNA tests look at genetic markers found in the 22 chromosome pairs which contain randomly mixed DNA from both parents, basically all chromosomes except the sex chromosome. Autosomal DNA contains almost the entire genome, or blueprint, for the human body; where we find the genes that determine our physical characteristics, from hair color to disease susceptibility. Because autosomal DNA is inherited by both men and women from both parents and all four grandparents, it can be used to test for relationships in all family lines. As a genealogy application, autosomal testing was originally introduced as a tool for determining biogeographical origins, or the percentage of various population groups (African, European, etc.) that exist in your DNA. Several testing labs, however, now offer extended family autosomal testing, which can help verify biological relationships through the grandparent generation.
Learn more: Autosomal Testing for Genealogy
Which DNA Testing Company Should I Use?The answer, as in many areas of genealogy, is "it depends." Because different people test with different companies, many of which maintain their own databases of tested individuals, you will achieve the greatest chance of useful matches by either being tested, or sharing your DNA results, with as many companies as possible. Some companies do allow you to enter results from outside DNA tests into their database, while others do not. If you can only afford to be tested by one company, then the International Society of Genetic Genealogists (ISOGG) has fairly up-to-date charts and information in their wiki for comparing the testing offered by different companies to help you choose the right company and test for your goals:
- Y-DNA testing comparison chart
- mtDNA testing comparison chart
= Autosomal DNA testing comparison chart (which doesn't yet include AncestryDNA autosomal testing as of 9 July 2012)