Without going into a detailed discussion (some helpful links below for more information), here's a brief explanation of how we use DNA testing for discovering if/how we are related to each other.

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There are basically three types of DNA test:

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Y-DNA, which tracks the direct male line. Only males possess a Y chromosome so they are the only ones who can submit DNA for Y-DNA testing. This is the main type of test we use in the Park/e/s DNA Surname Project. Family TreeDNA (FTDNA) is the only DNA testing company to offer the Y-DNA test.

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There are two types of Y-DNA test. For many years, we compared the results of STR (stir) markers, looking at repeated patterns of the basic components of DNA. If the patterns of two or more males matched, either perfectly or within a certain range of difference, we could determine that they shared a common male ancestor. Mutational differences in some of those repeated patterns allowed us to identify when related lines branched off from each other. 

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More recently, a newer type of Y-DNA test looks at a different type of mutation that occurs on the Y chromosome over time. These mutations are called SNPs (snips) and are extremely valuable in determining when branches of a related lineage split off in time. This is called the Big Y 700 test and is only offered by FTDNA. 

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Autosomal DNA, or atDNA. This is the DNA found on everyone's 1--22 pairs of chromosomes, with one half of each pair inherited from the mother, the other half from the father. Thus, we inherit atDNA from our parents on both sides, our four grandparents, our eight great grandparents, and so forth going back in time. Everyone has atDNA and can take this type of test. This is the type of test offered by Ancestry, 23andMe, FTDNA's Family Finder test, and others. 

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Mitochondrial DNA, or mtDNA. This is DNA we inherit from our mother, and it tracks the direct female line. Both males and females inherit their mother's mtDNA, but only females can pass it along to their children. Both males and females can take a mtDNA test. At present, we have not utilized mtDNA testing to any extent in our Park/e/s research.

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