From CSI to The Maury Povich Show, DNA and DNA testing has become a part of American popular culture. But what is DNA?
In simple terms, DNA is a string of proteins that contain coded blueprints for our bodies. It tells our bodies how to grow. We inherit our DNA from our parents, which is where its genealogical value comes in.
Right now, there are two basic kinds of DNA testing for genealogical purposes: Y-chromosome testing (Y-DNA) and mitochondrial DNA testing (mtDNA).
The Y-chromosome is passed from a father to his sons. In essence, it is what makes men, men. Women do not have, and thus cannot pass on, the Y-chromosome (though your brother, father, uncles and male cousins do). Y-DNA testing will reflect your father’s father’s father’s father’s father’s . . . father’s line. In many cultures, this is the same line that carries the surname, though this does not necessarily apply to African-Americans whose surnames only date back to the eighteenth or nineteenth century.
On the other hand, if this Y-DNA heritage contains a man of European descent, such as a previous slaveowner, the Y-DNA test provides hard scientific evidence of this heritage, as well as identifies the actual biological line – both facts that are extremely difficult to prove through traditional genealogical research methods.
Mitochondrial DNA (mtDNA) is almost the exact opposite of Y-DNA, in that it is passed from mother to daughter. Both men and women carry mtDNA and can test it. However, mtDNA has a much slower rate of mutation than Y-DNA, which, in plain terms, means that the results will reflect much greater period of time. For example, while a Y-DNA match may reflect, say, twelve generations back, an mtDNA match may reflect thirty or so.
DNA testing of both types, popularly called "genetic genealogy" or "genetealogy," consists of assigning values to a specific set of “markers,” set locations on a strand of DNA, whose mutation rates are relatively low. By comparing these values with those of others in the many DNA databases, you will find some “matches” with a low “genetic distance,” meaning fewer mutational differences. With both tests, the closer the match, the more recent the connection.
For more information on genetic genealogy and DNA testing, visit the International Society for Genetic Genealogy. The Genetic Genealogist blog is another very good source for up-to-the-minute news and commentary of DNA testing and genetic genealogy issues. The author of this blog also offers a free e-book entitled, “I Have The Results of My Genetic Genealogy Test, Now What?"
In a blog entry from 19 October 2009, Dr. Rick Kittles, the founder of the African Ancestry DNA-testing company, related that, “[w]hen we test the paternally inherited Y chromosome DNA we find that 3 out of every 10 (30%) African American men have European Y chromosomes while less than 5% of the maternally inherited mtDNA is of European ancestry.” Though mitochondrial DNA mutates at a much slower rate than Y-DNA, and thus reflects a much more distant past, this statistic does also to some degree reflect the practice of white slave owners siring children with their female slaves.
However, this also provides a unique opportunity for research for that 30% of African-Americans whose Y-chromosome ancestry shows European blood. The Y-DNA test result databases contain a wealth of information on the thousands of men of European descent who have submitted tests. Many of these men have traced their surname (Y-DNA) line back to a period confirmable by these DNA results. By comparing the markers of an African-American male with a European haplotype across the Y-DNA database, one might be able to confirm the paternity of “mulatto” slave ancestors, as well as identify a former slave owner. Both of these are extremely difficult tasks using record documentation alone. However, the precedents already exist for using Y-DNA tests in this manner, both in confirming a relationship between the Y-DNA of Thomas Jefferson’s family and descendants of Sally Hemings, and more recently confirming the descendance of Roots author Alex Haley from a slaveowner named Baugh.
The use of DNA testing for genealogical purposes is still in its relative infancy, and the potential for further developments in the future is limitless. At the current rate of advancement, we may see, in the near future, an even greater reliance on the biological record, to supplement and augment the written record. The biological record held in the DNA of every one of our cells may reveal even those genealogical answers that the written record does not.
For more information on "genetic genealogy" read the book a Trace Your Roots with DNA: Use Your DNA to Complete Your Family Tree
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