by Dr. Hsien-Hsien Lei
Posted December 12, 2007 in DNA and Genealogy
Recently, there have been a slew of articles decrying genealogy DNA tests as scams. Blaine at The Genetic Genealogist has covered the controversy in depth. And today, I’ve invited author Jon Entine back to Eye on DNA to share his thoughts on genetic genealogy. As you can see, it is possible to recognize the power of genetic genealogy as well as its limitations without writing the whole thing off.
What can DNA genealogy tests really tell us?
by Jon Entine
I was bemused by the headlined stories over the past month touting new genetic genealogy services, including the start-up, 23andME, launched by the wife of the founder of Google, and AfricanDNA, the brainchild of Harvard scholar Henry Louis Gates, Jr. in cooperation with FamilyTreeDNA. According to 23andME, its service will â€œshed new light on your distant ancestors, your close family and most of all, yourself.â€
But what do these services really offer? I have more than a passing interest in this question because my recently published book, Abrahamâ€™s Children: Race, Identity and the DNA of the Chosen People, is the first of a new genre: using DNA to help us connect with our common ancestorsâ€”our ethnic identities. DNA can do that. The more responsible genetic genealogy testing firms, like FTDNA, are very clear about what current technology can do. What DNA testing services canâ€™t do, however, at least not yet, is provide the average identity seeker with anything but a vague snapshot of our personal genetic profile and ancestry.
Remember a few years ago when Adrian Targett, an English schoolteacher, was linked by DNA to a 9,000-year-old skeleton found in a cave near where he lived in Cheddar, a tourist town famed for the distinctive cheese made there. â€œCheddar Man Found Alive in South of England,â€ touted one headline. Well, not really. The genetic testâ€”identical to some of the tests sold to the public today by commercial firms–indicated only that the two were linked to the same female ancestor. In kinship terms, they were cousins approximately 450 times removed. But they share only a few bases out of more than 3 billion nucleotide pairs in the human genome. Applying exponential math, Targett has inherited the DNA from many trillions of other relatives as well (though because of intermarriage among cousins and community members, the actual number of his ancestors is far less). His relationship to Cheddar Man is certainly fascinating and important for researchers, but itâ€™s genealogically tenuous, to say the least.
Going back ten generations we each have about 1,000 ancestors, which means we share about one millionth of a random neighborâ€™s DNA by direct descent. Twenty-five generations ago, about the time when Columbus happened on the shores of the Americas, the number of our potential ancestral cousins swells to an astronomical 30 million, almost all of the worldâ€™s population at that time. Yet, we have only one continuous male and female lineage. The male and female lines have become popular markers of identity because of the historical importance of surnames and the fact that these two DNA lineages are so easy to track. Yet, they are only two of millions of ancestral lines that we each carry. Many millions and perhaps billions of people living today are genetically linked to Cheddar Man, although that extremely distant connection might not show up in the few sections of the DNA that current technology can track.
This vast majority of the human genome, which amounts to more than 99 percent of our DNA, remains beyond the reach of current commercial DNA tests. Services such 23andME do provide glimpses of this genetic bounty but the information is virtually meaningless. Yes, its reports may indicate that we have a gene that is linked to weight gain, ear wax build up, or IQ, but even these seemingly simple traits are rarely the result of individual genes. There are more than 10 million tiny differences, known as single nucleotide polymorphisms, or SNPs scattered across the 23 pairs of human chromosomes and potentially interrelated in a myriad of ways. They are activatedâ€”â€œexpressedâ€ is the term used by geneticistsâ€”by gene-gene and gene-environmental interactions.
Make no mistake about it. Genetic genealogy is fascinating and it provides scientists with greater insight into our distant ancestors. We are also learning more and more about diseases, which is particularly of interest to Jews, who are subject to more than 40 disorders as a consequence of their separatist history. In fact, Bennett Greenspanâ€™s FTDNA is launching an Ashkenazi Genetic disease panel this week that will test for 25 common Ashkenazi diseases for only $500, an example of the responsible use of genetic genealogy.
But for the vast majority of us, DNA genealogy is little more than expensive entertainment, and potentially misleading. Those in search of certifying their identity or evaulating behavioral quirks using DNA tests may find disappointment as much as illumination. For example, in my book, I mention the case of Lisa Black, a systems administrator in Oakland who is African American. She was shocked to find that the DNA lineage that current technology can track, her female ancestors, was a blend of Native Americans, Chinese, and Sardinians. It came as a major blow to a veteran of the Black Power movement of the 1960s. â€œFor me to have a whole half of my identity to come back and say, â€˜Sorry, no African here.â€™ It just negates it all. â€¦ What does this mean? Who am I then?â€
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