Source: http://thelegalgenealogist.com dated 22 Feb. 2017
This article was written from a Eurasian perspective. The definitions are correct.
The genetic genealogy glossary defiunition of haplogroup is “a genetic population group of people who share a common ancestor on the patrilineal or matrilineal line. Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations.”
Okay. Great. What’s that mean?
Basically, if you think of all humans who’ve ever lived as part of the human race as a family tree, our haplogroup is what branch of the tree we can park ourselves on.
Everybody — male and female — has at least one haplogroup: our maternal haplogroup, as defined by our mitochondrial DNA (mtDNA). That’s the kind of DNA we all inherit from our mothers and that only females pass on to their children.Our mtDNA haplogroup, then, is the branch of the tree we’re sitting on when the roots go back to the first woman from whom we descend: our mother’s mother’s mother’s mother.
By itself, the mtDNA haplogroup tells us a great deal about our very deep ancestry many generations, even thousands of years in the past. But it also has some information we can use right now. It can tell us, for example, if our direct maternal line is of recent African or Native American origin. Or whether you, like me, have a maternal line that’s plain vanilla European.
Note that the fact that my maternal line is plain vanilla European doesn’t rule out having some more interesting ancestor from Africa or with Native American origin — it just means it isn’t my direct maternal line. It’s not in the direct line from my mother’s mother’s mother’s mother.
Only one of the major genetic genealogy companies offers mtDNA testing: Family Tree DNA. When you test at the HVR1 or HVR1+2 levels, the test looks at enough of the genetic markers to tell you what broad branch you belong to, represented by a letter like K or H. To get the specific branch — or twig! — the full mitochondrial sequence test (FMS) tests the entire mitochondria.
Men also have another haplogroup, carried in their YDNA. That’s the kind of DNA that only males have and that’s passed from father to son largely unchanged through the generations. The YDNA haplogroup, then, is the branch of the tree a male is sitting on when the roots go back to the first man from whom he descends: his father’s father’s father’s father.
By itself, the YDNA haplogroup tells the tale of deep ancestry just as the mtDNA haplogroup does, can indicate specific types of recent ethnicity — and is particularly useful genealogically to help distinguish between groups of men of the same surname: in my own research, for example, we thought our Shew line might be related to a specific Pennsylvania Shew line until we found that our line was haplogroup I and the Pennsylvania line was haplogroup R. Different branches of the human family tree entirely.
You will get a prediction of your YDNA haplogroup when you test with 23andMe and can get very specific YDNA haplogroup data from YDNA testing with Family Tree DNA, the only major genetic genealogy company that offers YDNA tests.