Understanding DNA


  • What is DNA?
  • How can DNA testing help genealogy?
  • My ancestors are all long dead. How do I get their DNA?
  • How does DNA testing work?
  • How conclusive is DNA testing?
  • Can I use DNA testing in lieu of other research?
  • Who should get tested?


    What is DNA?

    DNA or DeoxyriboNucleic Acid is the molecule sometimes known as the blueprint of life. It contains the genetic code that exists in each cell of our bodies and is found throughout nature in living things. Genealogists can compare certain sequences or markers on specific chromosomes between living individuals in hopes of finding common ancestors.
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    How can DNA testing help genealogy?

    For purposes of surname genealogy studies, DNA refers to the 23rd chromosome pair. Females have two x chromosomes, while males have one x and one y chromosome. The y chromosome is passed from father to son and is usually identical from father to son. Occasionally, there is a mutation. Over 1000s of years, these mutations have resulted in distinctive DNA profiles for different families. These differences are the focus of DNA testing in genealogy, often called yDNA.
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    My ancestors are all long dead. How do I get their DNA?

    Males carry the yDNA of their Surname ancestors, so we test them as representatives of their ancestors.. DNA tests are taken from the living and compared among groups of people. We look for male descendants who share a common surname or surname spelling variant. A single Y-DNA test is not that useful, but can be very revealing when compared to known or suspected cousins. In many cases, yDNA matches among individuals indicate a common male ancestor who may have lived hundreds of years ago, with the “cousins” being completely unknown to one another.
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    How does DNA testing work?

    The DNA test is typically a cheek swab, which collects tissue cells. The laboratory examines these cells and uses standardized protocols to count the number of repeats of genetic patterns at standardized locations on the DNA helix. A DNA result is a set of repeats (numbers) at particular addresses (markers). By comparing the numbers at the markers, we can determine if a man shares a common ancestor with a second sample. Typically, this is recorded as the number of exact matches and the total number of markers, i.e.: 12/12, 23/25 33/37, etc. Generally, for a greater number of markers, there is a higher reliability and for a closer the match in numbers, there is a closer relationship.
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    How conclusive is DNA testing?

    The typical researcher is interested in specific individuals in a specific family tree, while DNA testing evaluates common ancestry. By itself, a DNA test cannot confirm that a specific individual is the ancestor of the test participant.

    However, DNA testing can confirm that two test participants share a common ancestor. When combined with traditional genealogy, DNA results can aid in reconstructing genealogies and can confirm or refute specific relationships, including descent from specific ancestors, with a high degree of confidence. The most useful comparisons are between men who have closely matching yDNA patterns and who have also established paper trails (genealogies).

    DNA testing can be conclusive in proving that a male from an earlier generation is NOT an ancestor. The degree of certainty is a function of genealogies of the participants who document the earlier male.
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    Can I use DNA testing in lieu of other research?

    DNA testing should be used as a supplement to traditional research. It has a limited value when used alone.
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    Who should get tested?

    Anyone who is interested in confirming their surname ancestry should consider DNA testing. A male can represent himself and his surname family, while a female will need to arrange for a male relative to represent her and her family.

    Sooner or later, in researching a family tree, we all get to the point where the paper records become scarce to non-existent. Perhaps we have several possibilities or much circumstantial evidence as to whom the next ancestor in a line may be, but no way to determine which is which. DNA testing may be just the thing to help to break down some of those “brick walls,” which sooner or later, we all face.