For genealogical purposes, there are three main types of DNA tests that are available: Y-chromosome (Y-DNA) tests for the direct paternal line, mitochondrial DNA (mtDNA) tests for the direct maternal line, and autosomal DNA (atDNA) tests for finding matches on all your ancestral lines.
Each test type examines a different part of your DNA.
The diagram above depicts a typical human cell containing:
- The nucleus in the centre, which contains
- autosomal DNA (chromosome pairs 1-22; one of each pair is inherited from each parent)
- sex chromosomes (chromosome pair 23; one inherited from each parent)
- XX for females (an X from mother and an X from father)
- XY for males (an X from mother and a Y from father)
- Mitochondrial DNA in the cytoplasm (outside the nucleus), which everyone inherits from their mother.
The pedigree chart below shows how Y-DNA, mtDNA and atDNA are inherited in your family tree:
A Y-DNA test compares a male's y-chromosome markers with those of other males who have also tested, and will match up males with the same or very similar Y-DNA.
It is relevant to the direct paternal/male line only (generally the surname line), as per the blue boxes on the pedigree chart above - so it is ideal for use with surname projects.
Only males have Y-DNA, inherited from their father, through his father, his father, his father, etc, so only males can test for it.
A Y-DNA test can help determine if a male descends from the same male or line as another male who has tested, but generally can't tell you 'how', 'when' or 'where' in your tree you match, other than on the direct paternal line.
- Refer to Y-DNA: the Direct Paternal Line for more detailed information, pedigree charts and examples of how yDNA testing can be useful in your family history research.
A mitochondrial DNA test compares a person's mtDNA with that of others who have also tested, and will match up people who share the same or very similar mtDNA.
It is relevant to the direct maternal line only, as per the pink boxes on the pedigree chart above.
Everyone has mtDNA, inherited from their mother, through her mother, her mother, her mother, etc, so anyone of any gender can test their mtDNA. Males cannot pass it on to their children, but they can test their mtDNA.
A mitochondrial DNA test can help determine if you descend from the same female ancestor as someone else who has tested, but not necessarily 'how', 'when' or 'where' on your family tree you share that ancestor.
- Refer to mtDNA: the Direct Maternal Line for more detailed information, pedigree charts and examples of how mtDNA testing can be useful in your family history research.
An autosomal DNA test compares your autosomal DNA with the autosomal DNA of everyone else in the testing company's atDNA database, and provides you with a list of those people you match, with estimated relationships based on the amount/percentage of shared DNA.
Autosomal DNA tests include FTDNA's Family Finder, 23andMe, AncestryDNA, MyHeritage DNA, and matching is coming soon to Living DNA too!
Autosomal DNA testing can match you with relatives on ALL your ancestral lines - including the brown, pink and blue boxes in the pedigree chart above.
Everyone inherits autosomal DNA - directly from their parents - containing a random mix of DNA segments passed down from their grandparents, great-grandparents, great-great-grandparents, etc... so anyone of any age or gender can be tested.
- Refer to atDNA: Finding Matches on All Ancestral Lines for more detailed information, pedigree charts and examples of how atDNA testing can be useful in your family history research.
Autosomal DNA test results at some of the testing companies also include X-chromosome matches.
- X-DNA matches can be very useful, as specific inheritance patterns apply to the X-chromosome. Males can only inherit an X-chromosome from their mothers, whereas females can inherit some X recombined from both parents.
Identifying DNA relatives as X-matches can help isolate your shared common ancestor to particular branches of your tree, limiting the breadth of your research to find the connection.
- Refer to X-DNA's helpful inheritance patterns for more detailed information, pedigree charts and examples of how X-DNA matches can help with your research.
- Admixture: Autosomal DNA testing also includes a prediction of your ethnic makeup (known as 'admixture'), including maps of your ancestral population clusters/regions and estimated percentages. These are generally accurate at the broad continent level, but can vary at the sub-regional levels. As the reference databases are developed and updated (adding more detailed regions and more or better population samples for existing regions), your results will be updated automatically. Each of the testing companies presents their reports differently, often at different levels of confidence, and over different time periods.
There are numerous resources that cover the above topics in more detail, including websites, blogs and books. Refer to Genetic Genealogy Links & Resources for some of the easiest-to-understand resources.