Y-DNA STR testing: From Forensics, to Relationships, to Genealogy Testing

You’ve always been proud of your rather unusual last name, so one day when another man with the last name Quigley sits beside you on the plane, you are intrigued. A long conversation during the flight reveals that both of your great-great grandfathers were from Northern Europe and immigrated to North America three generations ago. You both agree that you might be related. At the end of the journey you exchange contact information and go your separate ways. Even a couple of weeks later, here you are still wondering, “Could I be related to this other Quigley?” There is a simple test that can solve this puzzle and it’s known as a Y-DNA STR marker test, which will help individuals to track their paternal lineage and find close and distance relatives on their paternal line.

DNA Ancestry testing for paternal lineage involves examining markers on the Y-Chromosome (Y-DNA) that tend to change, or mutate over time. To accomplish this, geneticists examine two types of markers found in the Y-DNA. One type of test examines extremely slow mutating markers called SNPs (single nucleotide polymorphisms) to identify ancient changes that occurred tens of thousands of years ago. The drawback of Y-DNA SNP tests is that it can only provide information on an individual’s ancient ancestry dating back tens of thousands of years but it will not provide any information regarding more recent ancestral events. For instance, two people wishing to determine whether they share the same paternal lineage over the past few hundred years won’t be able to do it with SNPs. In such cases, a different group of markers known as STRs (short tandem repeats) must be used. Y-DNA STR markers are small DNA sequences 2 to 13 nucleotides in length which are repeated many times in a row. STR markers have a much faster mutation rate compared to SNPs and this rapid mutation rate is useful for tracing more recent ancestry (such as searching for males with common paternal ancestors within the past 500 years or less).

We each inherit 22 autosomal chromosomes and one sex chromosome (X or Y) from each of our parents. Both men and women inherit an X-chromosome from their mothers. Daughters inherit a second X-chromosome from their father and sons inherit a Y-chromosome from their father. In that way, STRs on the Y-chromosome are passed down strictly from father to son and can be used to trace the paternal lineage.

Surnames are passed down from father to son in many societies, so Y-STRs tests are the best choice when trying to determine kinship between people with the same last name (such as the two Quigley’s) or searching for relatives who descended from the same paternal line. Comparing the Y-STR profiles of any two individuals determines if they descended from the same forefather and also indicates approximately how many generations ago any two men shared the same paternal ancestor, based on the “time to most recent common ancestor” (TMRCA) calculation. The TMRCA value is determined based on the mutation rates of STR markers, the number of STR markers compared and the number of matching STR markers. So with just a simple mouth swab and Y-DNA STR test, the two Quigley’s can quickly determine if they descended from the same forefather. Also, if they are choose to use existing ancestry databases, they will be able to search for individuals from around the world who have also descended from the same paternal lineage.

Whether you are a man who was adopted and have no information about your biological parents or someone wishing to research your family history, Y-STR testing may be a good starting point to finding your paternal origins. Once you find your first few matches, you can use those matches as a lead to investigate further. If you are the family genealogist you might want to use Y-STR tests for confirming family legends or solve family mysteries or search for family links. The Y-DNA STR marker profiles of many notable figures in history have also been determined, so if you just want to know whether you are linked to famous men (like Thomas Jefferson, Genghis Khan, or King Ramesses III), Y-STR tests can find those links.

Y-DNA STR marker testing is not only useful for genealogy, but is also used in solving relationship questions and forensics. While both paternity testing and forensic analysis rely on STR markers on the autosomal chromosomes, there are special circumstances when STR markers on the Y-chromosome become useful. In the case of unknown paternity of a male child where the assumed father is deceased, Y-STR testing from living paternal line descendants can be used to provide evidence of kinship. In forensics, Y-DNA STR marker testing is used when dealing with mixed samples. Because females do not have a Y chromosome, all contaminating female DNA can be excluded from the tests. Y-DNA STR marker testing was used to help solve the Boston Strangler case 50 years after the crime was committed.

The Y chromosome may be the third smallest chromosome, but over a hundred Y-DNA STR markers can be tested that are useful for paternal lineage analysis. The one caveat to this test is that only men can benefit from it since only men have a Y-Chromosome. Females wishing to investigate their direct paternal lineage using Y-DNA must test the Y-DNA of a direct paternal line relative such as a brother, father, uncle or cousin who is on their direct paternal line. Whether you chose to take the Y-DNA STR test to answer relationship questions, search for paternal line relatives or investigate matches to indigenous populations or famous people in history, Y-DNA STR markers are the one of the fundamental genetic markers for beginning the investigation of your paternal lineage.