"By mapping the appearance and frequency of genetic markers in modern peoples, we create a picture of when and where ancient humans moved around the world," explains National Geographic's Genographic Project, a DNA study collecting DNA samples from humans all over the planet.
The science behind SNPs and deep genetic ancestry is complex, and it can't tell you everything. But knowing where you fit in on the family tree of humanity certainly gives a broader, richer meaning to your own paper-trailed family tree.
What SNPs are and how they work
Very simply, a Single Nucleotide Polymorphism (SNP, pronounced "snip") is a genetic variation that is passed down from generation to generation in DNA. It becomes helpful to genealogists because not only is it inherited, but it's an unusual enough occurrence that it can be tracked as well. "SNP mutations are rare," writes Family Tree DNA, a genetic testing company. "They happen at a rate of approximately one mutation every few hundred generations."
Certain SNPs can be traced back to the population where the mutation first made its appearance. These populations are haplogroups, which National Geographic describes as "branches on the tree of early human migrations and genetic evolution." Haplogroups can be further divided into subclades.
What can SNPs tell you?
Knowing your haplogroup and subclade reveals your deep genetic ancestry; that is, where your ancestors lived and migrated thousands of years ago. Haplogroup R1b is commonly found on the west Atlantic coast, for example, while haplogroup O began in Asia roughly 35,000 years ago, branching into central and east Asia. Further SNP testing can reveal subclades, narrowing down geographic locations even further.
Although SNPs can't reveal recent genealogy, it can provide clues or an unexpected ancestral detour. One Genographic project participant, whose English grandmother had dark skin and many Gypsy friends, felt it was safe to assume her grandmother was also of Roma descent when their mitochondrial DNA was revealed to be a southwest Asian haplogroup.
Another project participant of Sicilian descent ended up, instead, narrowing his subclade down to an area around England, northern France and the Low Countries. While he assumes the migration to Sicily occurred in the last 1,200 years (based on two other Italian members of his specific cluster), DNA can't tell him when, how or why.
What SNPs can't tell you
SNPs describe broad movements and locations of people thousands of years ago, and while they are also tested through the paternal Y chromosome or maternal mitochondrial DNA like other genetic tests, they don't provide the recent history that other genetic tests do.
And while one Genographic participant was able to come to an ethnicity conclusion based on her maternal ancestor's appearance, habits and haplogroup results, it is inaccurate to believe that SNP testing alone will necessarily confirm a specific ethnic or cultural identity. "Haplogroups are not cultural groups," advises the International Society of Genetic Genealogy, "although a haplogroup can be strongly represented by a cultural population such as American Indians."
The Genebase blog is even more blunt. "No, your haplogroup will not tell you if you are Welsh or Irish. It will not tell you your ethnicity. Although there are associations between ethnic groups and haplogroups, you must remember that haplogroups represent deep ancestry, tracing events from tens of thousands of years ago."
Also, because SNP testing is done on mitochondrial or Y chromosome DNA, not all of a person's genealogy lines can be tested. Someone can find out the haplogroup for his father's father's father's line, or her mother's mother's mother's line, but to learn the deep ancestry of your maternal grandfather or paternal great-grandmother will require finding a relative who is descended from them exclusively through a maternal or paternal line.
So why test for SNPs?
Knowing your haplogroup and subclade, even for a few of your many ancestral lines, gives you an exciting look at what your ancestors did long before any genealogical paper trail came into existence. Many people also find that their sense of family expands to include millions of other people, if not all of humanity.
"When I see other people, I feel an even stronger connection to them now," writes one of the Genographic participants. "We're not just siblings in spirit. We really are related, no matter how distantly."
There are several tests available, at varying prices, to discover your haplogroup. The kit through the Genographic project costs $99.95 plus shipping, handling and any applicable taxes. The project will perform one test of your choice on the sample you provide (mtDNA or Y chromosome). For more information, visit http://genographic.nationalgeographic.com.