The Y-DNA Test for Genealogy

 Y-DNA Testing for Genealogy
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. (If there were no changes, [see mutations below] each man would have exactly the same yDNA as "Adam" and with each other.) .
♦ Because yDNA is passed down from father to son, just as surnames are passed down in western societies, it is pretty easy to visualize - and to track through genealogy.  This is why yDNA projects are organized around surnames.
♦ All men who share the same "common ancestor" will carry essentially the same yDNA and receive tests results that are also essentially the same.
How it's done
  • 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).
  • yDNA results are reported as a string of numbers, with each number representing the count at a specific address.
  • 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. 
  • By comparing the closeness of the string of numbers, we can draw conclusions on which men share a common ancestor and estimate (but with a disappointingly wide range) when this common ancestor would have lived.
  • 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.
Why yDNA testing is useful
  • DNA testing can confirm that two test participants share a common ancestor.  By itself, however, a DNA test cannot confirm that a specific individual is the ancestor of the test participant.
  • 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).
The rules for yDNA testing
  • The yDNA test is used for testing males only (males have one x and one y chromosome).
  • Surname Projects use yDNA test results.
  • Females cannot take a yDNA test, but they can make use of this test if they can convince a male relative to yDNA test for this surname line (females have two x chromosomes and no y chromosome).
  • This test is only useful in tracing the male participant's father's father's ... father's line.
  • A male researching a line that came down to him through a female can arrange to test a male relative to represent her line. (His yDNA came to him through his father's father's...father's line.)
Y-DNA Haplogroups
  • Fortunately, there are random and subtle changes (mutations)that allow us to see differences in different "genetic families".
  • Using these differences, scientists have been able to group all men into major branches called "Haplogroups".
  • These can be arranged into a "family tree of man" that shows the different branches that have separated over 1000s and 10,000s of years, far before there were surnames.
  • Each man today can be assigned to a Haplogroup, which tells him his "deep, ancient ancestry".
  • Many men's haplogroup can be estimated by looking at their results, while others have to have a test done called the "SNP test" (pronounced "snip")
yDNA is passed from father to son "essentially unchanged". However, on a random, but predictable basis for a large group, minor changes occur that we call "mutations".
  • These slight changes 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.  (Our genealogical paper trails usually extend a few hundred years, with a fortunate minority having paper trails reaching back 400 years or so. And, there a very few who have paper trails reaching back as much as 1000 years or more.)
  • We cannot predict when these mutations will occur in an individual family, but we do know that a mutation that occurs in one man will be passed on to his sons - and that they will pass it on to their sons, and so on ....
  • As an example: one man may have an 11 at specific address, while another man who shares the same common ancestor may have a 12 at the same address. This means that somewhere in the line of one of these men - and after their most recent common ancestor - a mutation occurred to change the count at that address for one of the men's family, but not the other.
  • These mutations have occurred through the centuries, giving us the Haplogroups mentioned above.  Scientists are continuing to study Haplogroups and are beginning to break them down into smaller and smaller sub-groupings.  
Test Options
You can be yDNA-tested at different "resolution" levels (12, 25, 37, 67, or 111 markers). 
  • FTDNA strongly encourages group testing - often called testing through your "Surname Project".
  • Other examples of a group project are the Clan, Family, Geographic, Regional and Ethnic projects. 
  • Ordering your yDNA test through a project gives you a lower test price and automatically makes you a member of the project. 
  • If there is a project at FTDNA, then you can order there and be tested at the group rates.
Choosing the right yDNA test: 
Learn more about choosing a yDNA test.