Just as a point of interest: I tried to find an appropriate image for Y-Adam, like the one for Mitochondrial Eve. Do you know what happens when you put “Y-Adam” into a search engine and look for images? You get a LOT of photos of Adam Levine.
Another type of DNA that genealogists may find useful in their ancestor hunts is Y-DNA. Y-DNA is passed down from the father only to his son. Unlike the mother who passes on her mtDNA to all her children, Y-DNA is unique in that it stays only within the patrilineal (father to son) line. Y-DNA is passed identically from father to sons through the Y chromosome that determines gender. Remember, men pass down either an X or Y chromosome that determines the gender of the baby. When dad passes down his X chromosome, the baby is a girl; if he passes down the Y—which is where Y-DNA is contained—then the baby is a boy.
As with moms and mtDNA, it is possible to follow Y-DNA through the male ancestors in dad’s line. Y-DNA can lead to identifying MRCAs (most recent common ancestor) for DNA matches and can help prove family trees are on the right track. Y-DNA follows the same rule as at- or mtDNA: Alone, DNA is not proof of relationship but it can strongly support genealogical research.
Y-DNA is a little different to test than either at- or mtDNA, which are each a single test to determine results. Y-DNA tests look at sequences called short tandem repeats (STRs, also called markers) within the chromosome. Each person has a unique number of repetitions of STRs and that number is called an allele (sequence of the gene) of the marker. Repeated sequences of nucleotides (basic structural unit of DNA) in Y-DNA are counted and the number of repetitions become the assigned value.
Y-DNA tests tend to be sold based on the number of markers (STRs) that it checks. Those with a simple interest in basic information might be well served by a lower number of markers (and lowest cost). Those looking to research their surname line might do well with a middle-of-the-road number of markers. If you are looking for a specific match, such as a bio father, testing the highest number of markers would likely be the most beneficial for you. I’m being cagey in talking about the testing services for two reasons: First, I’m hesitant to recommend any one testing site over another but, at this point in time, I would recommend one of the more well-known, long-term companies; second, my focus in “Plain English Genetic Genealogy” is atDNA but I recognize it is helpful to have some knowledge of other DNA tests that can assist in genealogical research, hence the detour into mt- and Y-DNA.
Okay. So, what does dad give you when you get your Y-DNA from him (assuming you’re a son, of course)? Besides the potential for matching others in your pop’s line, you get your Haplogroup, that thing I mentioned a bit in my mtDNA blog. So, let’s talk migration.
Let’s go with the accepted understanding that humans began in Africa. As homosapiens grew in numbers, some people decided to look for new environments—whether for economic (resources), social or adventurous reasons—and so went off in groups to discover the world.
Here’s a visual of the journeys the major haplogroups took; notice that National Geographic folks indicated with a gold star where Y-Adam—yes, there is a Y-Adam, just like there is a Mitochondrial Eve—most likely lived.
This National Geographic map looks kind of confusing, I get that, but populating the planet is a long, confusing project. One way to follow your journey is to test your Y- or mt-DNA and learn which Haplogroup(s) are yours. Just like using unique identifiers to determine matches to regional signatures with atDNA, signatures (markers) in Y-DNA can identify the route your ancestors took.
Just like with Mitochondrial Eve, it is possible to trace back—using the same concept of mutations (changes) in Y-DNA—to make a best guess who is the father of all homosapiens (humans) living today. It is suspected that Y-Adam lived more than 200,000 years ago. Again, as with Mitochondrial Eve (suspected to live about 140,000 years ago), many lines of Y-DNA do not get passed down. A man with no sons and only daughters cannot pass his Y-DNA down; a man with no sons who survive to fatherhood will not pass his Y-DNA down. So, the Y-DNA that a father’s father passes on to him, stops when no male children have male children of their own.
Once you have your Y-DNA and your Haplogroup, one of the things unique to Y-DNA is the ability to trace surnames through the ages.
Since women traditionally took the names of their husbands, this is not really possible with either mtDNA (passed from mom and whose daughters pass it to their children) or atDNA (received from both parents). Like surnames, Y-DNA is passed down and retained from father to son.
If your name is Smith, Jones, Clark, Johnson, etc. this is an extraordinary tool to assist in your genealogy. When faced with hundreds (or more) of Smiths, testing your Y-DNA will help identify to which group of Smiths you belong. Imagine the possibilities with this one tool.