Y-DNA Testing

The Basic Science

  • Because males carry the yDNA of their surname ancestors, we can test them as representatives of their ancestors. Each man gets his yDNA from his father, who got it from his father…all the way back.
  • These Y chromosomes are passed from father to son virtually unchanged. Over time, there may be slight changes, or “mutations”, which occur during replication of cell DNA, but the majority of Y-chromosome DNA remains the same. When a mutation does occur, all male descendants of the man carrying the changed Y-chromosome DNA will have that mutation. When a second mutation occurs, all of that man’s descendants will carry that mutation as well as the first one, and will be a distinct sub-group of the group with the first mutation.   Essentially, these represent "branches" on the human Y-chromosome DNA tree.
  • These mutations occur at intervals that are especially useful for genealogy and are the focus of yDNA testing in surname genealogy. 
  • The laboratory examines the DNA sample and uses standardized protocols to count the number of repeats of genetic patterns at standardized locations on the DNA helix. A yDNA result is the number of times a specific pattern repeats (alleles) at particular addresses (markers).
  • A single Y-DNA test is not that useful, but by comparing the numbers at the markers against other men’s test results, we can determine if a man shares a common ancestor with a second sample.
  • Generally, there is a higher reliability at a higher number of markers, and the closer the match in numbers, the closer the relationship.  The more markers in common, the more likelihood of a common ancestor. 
  • 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.
  • DNA testing can also be conclusive in proving that a male from an earlier generation is NOT an ancestor and that two males do not share a common ancestor.
  • The most useful comparisons are between men who have closely matching yDNA patterns and who have also established paper trails (genealogies).