Family Tree Magazine http://www.familytreemagazine.com/article/DNAtests-for-ethnic-origins

What the AncestryByDNA test can tell you about your ethnic origins. In an earlier, less-enlightened era, "racial purity" was highly valued (at least among the race that mostly ran things), and ugly phrases such as "half-breed," "mongrelization" and "race mixing" were hurled like curses. Today, though bad, old attitudes still linger in dark corners, golf fans root for Tiger Woods, Cher can boast of her Cherokee blood, and genealogists look for exotic rainbows in their roots. Even as ideas about race have changed, new tools have evolved for studying the subject. Some geneticists now argue, in fact, that the whole concept of race isn't really biologically relevant, that the DNA differences underlying our racial divisions are, well, microscopic. Others are using advances in DNA technology to probe the racial mixture of the world's populationand discovering, yet again, that we're more similar than we are different. As Tony Frudakis, a molecular biologist and CEO of DNAPrint genomics in Sarasota, Fla., puts it, "In all of us, especially in the US, there is a continuum of ancestries." A branch of Frudakis' company called AncestryByDNA aims to help genealogists explore the racial mix of their family trees with a simple DNA test. Unlike other DNA-testing kits, AncestryByDNA does not rely on Y-chromosome tests (which only males can use) or mitochondrial DNA. Instead, it looks at a person's Single Nucleotide Polymorphisms (SNPs, or "snips" for short)—think of them as collections of letters among the long sentences of the human genome. Then, AncestryByDNA compares your SNPs to a database of results representing four main human racial groups, based on continent of origin: sub-Saharan African, Indo-European (Europeans, Middle Easterners and South Asians, such as Indians), East Asian (Japanese, Chinese, Koreans, Pacific Islanders) and Native American (ancient migrants to both North and South America). Originally, the test used six groups, distinguishing South Asian from European and Pacific Islander from East Asian, but the current version retreats from that until further refinement in an upcoming version 3.0. AncestryByDNA simply places your DNA along this racial spectrum, which means the test can't connect you with distant DNA cousins, as some genetic-genealogy offerings promise. But if you've always wondered if you have some African roots, for example, AncestryByDNA offers an easy way to put your theories and family stories to the test. At $158 for an individual, it's cheaper than most DNA tests for genealogy, which typically run $200 to $300. And unlike tests that require Y-chromosomes, you don't have to have the cooperation of a male family member. The test itself couldn't be simpler. When you order, you get two sterile Gene Guard swabs, which look sort of like small dental instruments. You scrape the inside of each cheek with a serrated swab at least 10 times, using an up-and-down motion and moderate pressure. Then, let the swabs briefly air-dry and pop them in the supplied return envelope. A few weeks later, you'll receive a CD-ROM that includes a certificate and results table showing your ancestral proportions, a triangular graph charting your results and a map of ancient human-migration patterns http://www.familytreemagazine.com/article/DNAtests-for-ethnic-origins

http://www.slate.com/articles/health_and_science/science/2006/03/how_african_are_you.html

The newer "genetic admixture tests" examine DNA from genes inherited from all of a person's grandparents, great-grandparents, and so on. A few of these genes reflect the part of the world where those ancestors lived. Like postcards, they track the movement of people from the lands of their ancestors to their current address. Scientists studying these genetic variations now focus on sites that vary between people by one chemical letter. They're called "single nucleotide polymorphisms," or SNPs. Some of these SNPs are important: They may contribute to traits like skin color or resistance to regional diseases like malaria. Others vary among populations just because of chance. For geneticists, finding the SNPs that mark populations is a challenge. For the most part, the same SNP might be found in Africans, Europeans, and people from every other part of the world. It's now possible to test quickly for hundreds of SNPs by using special microchips that bind to the distinctive DNA sequences. These tests examine hundreds of SNPs at once; if among these a person has many that are common in Africa, it is likely that she has some African ancestors. Admixture testing works best in groups like African-Americans, whose ancestors in Africa and Europe lived far from each other. Most of the ancestry of today's African-Americans can be traced to West or Central Africa, with a minority from other parts of the continent. (Gates' family is a bit exceptional in terms of origin.)