Genealogy testing uses a sample of your DNA to trace your ancestry, find living relatives, and estimate your ethnic background. You provide a saliva sample or cheek swab, mail it to a testing company, and receive results that can reveal family connections going back several generations and migration patterns stretching back thousands of years. The technology has become one of the most popular consumer science products available, but the different test types, what they can actually tell you, and their limitations are worth understanding before you spit in a tube.
How the Three Test Types Work
Not all genealogy tests look at the same parts of your DNA, and the type you choose determines what kind of ancestry information you get back.
Autosomal DNA tests are the most common and the most versatile. They analyze the 22 pairs of non-sex chromosomes you inherited from both parents, roughly 50% from each. Because this DNA comes from both sides of your family, autosomal tests can identify relatives on any branch of your family tree. The trade-off is depth: they’re reliable for finding connections within about five to six generations (your third or fourth cousins), and their power drops off sharply beyond that. Ten generations back, roughly 250 to 300 years ago, you could have up to 1,024 ancestors, but each one contributed less than a thousandth of your genome. By fourteen generations back, there’s a greater than 95% chance that any given ancestor left no detectable trace in your DNA at all.
Y-DNA tests trace your direct paternal line: father to father to father, as far back as the records go. The Y chromosome passes from father to son without shuffling, so it stays remarkably stable across generations. This makes it useful for confirming surname-line connections and for tracing your paternal ancestors’ migration routes going back thousands of years. Only people with a Y chromosome can take this test directly, though women can have a male relative (father, brother, paternal uncle) test on their behalf.
Mitochondrial DNA (mtDNA) tests do the same thing for your direct maternal line: mother to mother to mother. Mitochondrial DNA sits outside the cell’s nucleus, separate from your 23 chromosome pairs, and mothers pass it to all their children without recombination. Both men and women carry mtDNA, so anyone can take this test. Like Y-DNA, it can trace deep ancestry going back thousands of years, but only along that single maternal line.
What You Actually Do
The process is simple. Most consumer testing companies send you a kit that uses either a saliva spit tube or a cheek swab. Unlike blood samples, which need to be processed quickly, saliva samples are stable at room temperature for weeks to months, making mail-in collection practical. You register the kit online, provide your sample, and send it back in a prepaid mailer. Results typically arrive in four to eight weeks, depending on the company and test type.
How Ethnicity Estimates Work
The ancestry percentage breakdowns you see in your results (for example, “42% Western European, 28% West African, 18% Indigenous American”) come from comparing your DNA to reference panels. These panels are collections of DNA from people with deep, well-documented roots in specific regions. The testing company’s algorithm looks at hundreds of thousands of genetic markers across your genome and statistically matches segments of your DNA to the populations in their reference database.
This process is genuinely useful for broad strokes, but it has real limitations. Your results depend entirely on who’s in the reference panel. If a company has a large, well-sampled reference group for Scandinavian populations but a smaller one for, say, Central Asian populations, the precision of your estimate will differ accordingly. Companies also update their reference panels over time, which is why your ethnicity percentages can shift when you log in after an update. Think of ethnicity estimates as statistical approximations rather than precise measurements.
Making Sense of DNA Matches
Beyond ethnicity, autosomal tests identify other people in the company’s database who share segments of DNA with you. The amount of shared DNA is measured in centimorgans (cM), and the number tells you how closely related you are. Full siblings share an average of about 2,613 cM, though the range runs from roughly 1,613 to 3,488. First cousins share an average of 866 cM (range: 396 to 1,397), and second cousins average 229 cM (range: 41 to 592).
Those wide ranges matter. Two people who share 400 cM could be first cousins on the low end or half-first-cousins or even great-grandparent/great-grandchild pairs. DNA testing companies suggest possible relationships, but the shared cM amount alone often can’t distinguish between several equally plausible connections. This is where combining DNA results with traditional genealogy research, such as family trees, records, and historical documents, becomes essential.
Kinship-inference tools can reliably estimate relationships up to about the sixth degree, which includes second cousins. Beyond that, the amount of shared DNA becomes too small and variable to draw confident conclusions from genetics alone.
Health Information in Genealogy Tests
Some testing companies offer health-related reports alongside ancestry results. In the United States, the FDA regulates these reports based on their medical significance. The agency has authorized consumer tests to report on several categories of genetic health information.
Carrier screening tests tell you whether you carry a gene variant you could pass to future children, even if it doesn’t affect your own health. Genetic health risk reports cover variants linked to conditions like late-onset Alzheimer’s disease, Parkinson’s disease, celiac disease, and selected BRCA1/BRCA2 variants associated with increased cancer risk. Pharmacogenetics reports provide information about how your genetics might influence your response to certain medications.
These reports screen for specific, known variants rather than performing comprehensive genetic sequencing. A result showing “no variants detected” does not mean zero risk for a condition. It means the specific variants the test looked for weren’t found. The FDA does not review ancestry-only tests, which are considered non-medical.
Privacy and Legal Protections
When you send your DNA to a testing company, you’re handing over some of the most personal data that exists. The legal landscape offers partial but not complete protection.
The Genetic Information Nondiscrimination Act (GINA) prohibits employers and health insurance companies from discriminating against you based on your genetic information. That definition is broad: it covers not just test results but also family medical history, use of genetic counseling, and participation in genetic research. GINA’s definition of “family member” extends all the way to fourth-degree relatives, including great-great-grandparents and first cousins once removed. Health insurers cannot use genetic information to raise your premiums, deny coverage, or make adverse decisions. Employers cannot use it to make hiring or firing decisions, and in most cases, they are prohibited from collecting it in the first place.
GINA has significant gaps, though. It does not apply to life insurance, long-term care insurance, or disability insurance companies. Employers with fewer than fifteen employees are exempt. And the law protects against discrimination based on genetic predisposition, not conditions that have already appeared. If you’ve been diagnosed with a disease, GINA’s protections for that condition no longer apply, though other laws like the Americans with Disabilities Act may.
Beyond anti-discrimination law, each testing company sets its own policies for data storage, sharing, and deletion. Some allow law enforcement to search their databases; others do not. Reading a company’s privacy policy and terms of service before testing is the most direct way to understand what happens to your data after you mail that tube back.
What Genealogy Testing Can and Cannot Do
Genealogy testing is powerful for confirming or discovering close family relationships, estimating broad geographic ancestry, and connecting with living relatives you didn’t know existed. It has helped adoptees find biological parents, revealed family secrets, and filled in gaps that paper records couldn’t.
It cannot tell you your ethnicity with decimal-point precision, reliably identify ancestors beyond about six generations, or replace traditional genealogy research. The DNA provides clues. Building a complete picture of your family history still requires combining those clues with documents, oral histories, and records. The most useful approach treats DNA as one tool among several rather than a definitive answer on its own.