Saturday, October 20, 2012

One set of cards we are dealt

kw: book reviews, nonfiction, genetics

I've been away for a few days, incommunicado, but I'm back, and with an immensely exciting book: DNA USA: A Genetic Portrait of America by Bryan Sykes. I had expected a "big data" study, with huge numbers of genomic analyses. Instead I found an intimate portrait limned by just a couple dozen "chromosome paintings", upon the background of genetic characterizations of the past decade or so.

One genetic portrait of the U.S., prepared according to the "ethnicity" reported in the 2000 Census, shows the ancestry that is most common in each of the counties of the U.S. and Puerto Rico:
This will be barely readable in this presentation. Click on it to see a much larger version. I was interested to see that the county in which my father and two generations of his ancestors lived is colored light blue, for German, and indeed he is some 25% German, while the county of my mother's origin is colored pale yellow, for "American" (meaning those who didn't claim a particular ancestry, but are presumably white Euro-Americans). Actually, for both my parents, a recent survey of known immigrants in our family tree reveals a slight plurality for English ancestry, but plenty of other countries of origin are mixed in.

The book is in three sections, though the third is brief. The background section describes the developments leading up to the present ability to do complete genome sequences, the meaning of the mDNA (mitochondrial DNA from mother lines only) and the Y chromosome (from father lines only), and, more pertinent to most of us, the ability to prepare a "chromosome painting" that shows the major elements of our ancestry in significant detail. A pair of chapters explains the very different reception certain people have given to genetic searching. In particular, Native Americans are very resistant to genetic studies, for both religious reasons and because they were very early exploited genetically, and are suspicious of the motives behind any such project.

The second section chronicles the expedition of Dr. Sykes with his son and wife, as they crossed the nation twice. Both directions they traveled by train; east to west it was Sykes and his son, and west to east, his son having gone off to start university studies, Sykes traveled with his wife. Over the course of the trip they collected saliva samples (about 15 ml in size) from more than twenty people, whose chromosome paintings are presented in the book's color plates. They also collected the stories of these people, many of whom had quite detailed knowledge about their family trees. Two of these volunteers were Native Americans, and the rest were evenly divided among Euro-Americans and African-Americans.

Chromosome painting is a service offered by 23andMe. It is based on half a million genetic markers, which keeps the price quite a bit lower than a total sequence would cost. While ancestry discovery is one popular service, they also provide a long list of genetic risks to which you might be subject, such as greater or lesser tolerance for lactose, or a susceptibility to certain cancers.

A chromosome painting (called an Ancestry Painting at the web site, I found), shows the positions of genetic markers of three types: European, African, and Asian. In the US, among most who are not of recent Chinese or Indian or Japanese (etc.) origin, "Asian" usually means Native American, because of their origin in Asia more than 15,000 years ago. This last point bothers many tribes, who hold the opinion that they have always been here, and some can get rather belligerent about it.

This chromosome painting, from the 23andMe web site, shows a portrait that is probably pretty close to my own: Mostly European (dark blue), with a few percent Asian (orange, and in this case representing Native American; it would be Cherokee in my case), and a smaller percentage of African (green). That is supposing that a certain great-great grandfather is who I think he is! The gray portions of the image are sequences that, for various reasons, cannot be pinned to any origin.

If my son's DNA were painted, it would be solid orange along the upper half of each bar, representing his Japanese mother. The lower halves would resemble a random decimation from my own painting: mostly blue, with a snippet of green and orange at most.

Interestingly, the ten or so Euro-Americans that were tested for this project were divided among New Englanders and Southerners. Most of the paintings for the Northerners were boring, solid dark blue. One had a tiny snippet of Asian DNA showing, and another had a bit of African. The author, being English, also has a single bit of Asian DNA, probably an actual Asian rather than a Native American somewhere in his family tree, but no more than eight or ten generations back. Then there were the Southerners. All had dribs and drabs of both green and orange in the dark blue. At least one found this distressing. The author wondered upon the outcome of testing a KKK member, and finding, say, 3% or so African ancestry, and a similar amount of "Asian".

There is an old joke about a man who claimed to be 1/3 Irish. When asked, "Isn't that impossible?", he said, "No, my dad is 2/3 Irish and my mom is all English." If you were to find that you were 2.77% Asian, what would that really mean? It is less than 1/32 but more than 1/64, but the way chromosomes cross over during the development of gametes isn't exact anyway. That 2.77% might be from a single Asian or Native American among your great-great grandparents, or it might be a little bit here, a little bit there, and so forth, among ancestors further back in time. A chromosome painting cannot ferret out such distinctions. For that you still need genuine genealogical study. However, if your family tree doesn't yet contain any Chinese or Cherokees, it indicates more digging is needed.

The book contains an appendix, with a brief summary of the "core mutations" of the mDNA clusters among Asian, African and European "founding mother" progeny. More details are presented in an earlier book, The Seven Faces of Eve. Guess what is next on my want list?

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