Saturday, November 3, 2012
A haplogroup is a population of individuals whom share a unique set of genetic markers that were derived from a common ancestor. All members of a haplogroup are descendants of a single man or woman that lived in the very very distant past. The Y-chromosome (Y-DNA) and mtDNA are the genetic structures that are associated with haplogroups. (The autosomal chromosomes are NOT associated with haplogroups.) Each mtDNA (maternal) and Y-DNA (paternal) haplogroup has a distinct set of genetic markers that define, distinguish and separate the different mtDNA and Y-DNA haplogroups. Your haplogroup, (L3e2a for example is a mtDNA subhaplogroup), is defined by unique set of DNA markers that's present on either the mtDNA or Y-DNA. Only members of the same haplogroup that you belong to have those distinct DNA markers. Every person has a mtDNA haplogroup and a Y-DNA haplogroup. In essence - a mtDNA haplogroup, such as L3e2a, represents a single woman that you are descended from who lived hundreds of thousands of years ago.
There are three basic mtDNA haplogroups - L, M, and N. The L haplogroup represents Mitochondrial Eve - an ancient and distant African woman. Mitochondrial Eve is the most recent common maternal ancestor of all current living humans. By definition, all of modern humanity fits into the L Haplogroup. As Mitochondrial Eve produced daughters, grand-daughters, etc, her original mtDNA sequence was copied and changed. This eventually produced the modern haplogroups that we see today. The L haplogroup is divided into seven subhaplogroups, L0,L1,L2,L3,L4,L5,L6. These six subhaplogroups (L0,L1,L2,L4,L5,L6) are found almost exclusively in Africa. This supports the notion that modern humanity began in Africa. Eventually modern humans traveled outside of Africa. The L3 mtDNA subhaplogroup represents that transition out of Africa. The M and N haplogroups are both descended from the L3 mtDNA haplogroup. Essentially all of the other mtDNA haplogroups which are found outside of Africa (A,B,C,R,T and etc) are descended from either the M or N mtDNA haplogroups. Haplogroups can be further subdivided into more subhaplogroups based on newly discovered DNA markers.
Similarly there are Y-DNA haplogroups with each given letters of the alphabet as well. Y-Chromosomal Adam represents the most recent common paternal ancestor of all living humans. By definition, all modern human men fit into the African Y-DNA Haplogroup known as the A Haplogroup. Haplogroup A is then split into the two major Haplogroups, B and CT, respectively. From the Y-DNA Haplogroup known as CT, the remaining African and Non-African Y-DNA haplogroups (DE, F, etc) are descended from.
Because of people's different religious histories, marital, and social practices, certain people tend to be strongly associated with certain haplogroups. For example, the A,B,C,D, and X mtDNA haplogroups are strongly associated with Native Americans. The R mtDNA haplogroup is present among 89% of Europeans. The Y-DNA haplogroup known as E1B1A is very strongly associated with African-American males.
It's important to understand that two or more people within the same haplogroup are related within an anthropological time frame (thousands of years), not necessarily a genealogical time frame (one to three hundred years). Two or more people may not share a recent common ancestor, but they still may share a distant haplogroup common ancestor. Your last (recent) common ancestor and your distant (haplogroup) common ancestor are two separate individuals. For example, my mother would be my last (not distant) common ancestor.
By the same token, two or more people can be in the same haplogroup and be related within a genealogical time frame. An example of this is seen among Native Americans. Having crossed the Bering Straits within the last 12,000 years, many Native American groups and circles have remained fairly small and are genetically similar enough to share BOTH matching haplogroups and recent common ancestors.
On the other hand, two or people may be in two different haplogroups, but still be related in a genealogical time frame. For example, my dad and I are in two different mtDNA haplogroups, but my dad is still my most recent common ancestor. This can be easily understood if one remembers that a haplogroup represents a single and separate distant side of a person's ancestry. A mtDNA haplogroup represents a single distant strict maternal ancestry (child -> mother -> mother's mother, etc). A Y-DNA haplogroup represents a single distant strict paternal ancestry (son -> father -> father's dad, etc)
Inferences From Haplogroup Assignments
A common practice is to make an inference about a person's ethnic composition, religion, and other socially defined information based on a person's haplogroup assignment. These inferences or conclusions are based on the frequencies of haplogroups. Basically the frequencies of certain haplogroups differs across certain populations. These frequencies exist because of the social practices, martial histories, and other social norms that many cultures exhibit.
For example - the Y-DNA haplogroup known as E1B1A7A has a very high distribution across Western Africa. The E1B1A7A has a very high frequency and presence among African-American males. This leads to a conclusion that a male who is E1B1A7A must be African-American. This is of course is not necessarily true. The E1B1A7A also has a distribution in South American as well.
As an another example - the Y-DNA haplogroup, known as R1B1A, has a strong presence and high distribution among European men. Yet my 2nd cousin - Lewis Lamar, who is considered African-American, has the R1B1A haplogroup. The E1B1A7A haplogroup is absent in his paternal lineage.
Such inferences drawn from a haplogroup assignment are very dangeous to make. The important concept to grasp and understand is that DNA does NOT define nor store information such as person's ethnic composition or religion. Those are socially defined concepts which are NOT defined by a genetic mutation. A person can no more be said to be 100% African or European from the DNA data alone.
Other forms of collaborating evidence would be required to confirm an individual ethnic composition, religion, or any other socially defined concept.
If anyone has any questions, please feel free to ask.