Posts filed under ‘science’

So what is genetic ancestry testing, really?

Genetic ancestry testing and the encompassing field of genetic genealogy have experienced somewhat of a boom in popularity in the past ten years. According to an article by Mark Shriver and Rick Kittles, genealogical research is one of the fastest growing hobbies in America (611). The advent and growing accessibility of biotechnologies have intensified this growth in interest in one’s genetic and genealogical background. By my count, at least twenty-five firms currently sell genetic ancestry tests over the internet, and it appears that hundreds of thousands of people are buying them. Blaine Bettinger, author of the popular blog “The Genetic Genealogist,” has estimated that over half a million consumers purchased genetic ancestry testing in 2008, and he predicts that this number grows by as much as 100,000 every year (Bettinger).

Consumers purchase and use genetic genealogy tools for a myriad of reasons. Some hope to identify relatives and connect with them through an established social network. Others aim to confirm existing genealogical records with genetic information. Many consumers hope to create a connection between their ancestral homeland or ethnic group (Bolnick). My personal reason is a bit less scholarly: I’m a technophile at heart, and I think genetic testing is amazingly cool. However, I do have access to a pretty significant archive of family history and genealogical records, and I’m looking forward to seeing if the family tree matches the genetic test results.

The science behind genetic ancestry testing

There are three main categories of genetic ancestry tests. Mitochondrial DNA (mtDNA) tests sequence or genotype part of the mitochondrial genome. There is an area of the mitochondrial genome that does not contain any protein-coding sequences, allowing mutations to freely accumulate without causing deleterious harm. This area, known as the hypervariable region, allows researchers and genealogists to study neutral genetic variation (Stoneking). Additionally, the mitochondrial genome is maternally inherited, and it exists and recombines separately from the nuclear genome and (Shriver). Because only female gametes contribute mitochondria, each person only has one mitochondrial ancestor per generation. Scientists have estimated the mitochondrial mutation rate, and when coupled with the amount of genetic variation between two mitochondrial sequences, one can predict how long ago the two sequences (which, presumably, belong to two individuals) shared a common ancestor (Devor).

The second kind of genetic test sequences or genotypes the Y-chromosome. Similar to mtDNA, Y-chromosome DNA does not recombine, making it a perfect source of markers for patrilineal genealogy (Shriver). This test can, however, only be done on those who have a Y-chromosome, which means I’m out of luck. I could get the results of my patrilineal ancestry if I convinced a male relative to donate his spit to my Responsible Genomics project, but that would require another $399 ancestry test. Looks like my full genetic genealogy will have to wait until later.

The third kind of genetic test uses ancestry informative markers on the autosomal chromosomes. These population-specific markers do not focus on a single lineage, as mtDNA and Y-chromosome tests do. Rather, these autosomal markers can be used to paint a picture of one’s ancestry from many different populations.

What Technology 23andMe Uses

23andMe offers genetic ancestry tests, as well as health-related genetic tests. For this project, I used the “Ancestry Edition” for the genealogy-only services. 23andMe uses Illumina’s HumanHap 550+ BeadChip technology, an array-based chip that analyzes over 550,000 single nucleotide polymorphisms, or SNPs.

23andMe takes the results of the SNP array and compares it to their reference database of haplotypes that have been identified in specific populations. 23andMe’s reference database is based on the Human Genome Diversity Panel and Illumina’s iControlDB database (Macpherson).

Now that I know more about what I’m really getting with my genetic ancestry test, I’m even more excited to receive my results! Let the waiting game begin!

Works cited in this post
Bettinger, Blaine. The Genetic Genealogist. 2008. Web. 12 Apr. 2010. http://www.thegeneticgenealogist.com/wp-content/uploads/InterpretingTheResultsofGeneticGenealogyTests.PDF.
Bolnick, Deborah, Duana Fullwiley, and Troy Duster, et al. “The Science and Business of Genetic Ancestry Testing.” Science 318 (2007): 399-400. Print.
Devor, Eric J. Mitochondrial DNA. Publication. Integrated DNA Technologies, 2005. Web. 1 Mar. 2010.
Macpherson, Mike, Werner, Greg, Mirza, Iram, et al. Global Similarity’s Genetic Similarity Map. White Paper 24-03. 23andMe. https://23andme.https.internapcdn.net/res/530/pdf/23-01_Estimating_Genotype_Specific_Incidence.pdf.
Shriver, Mark D., and Rick A. Kittles. “Genetic Ancestry and the Search for Personalized Genetic Histories.” Nature Reviews Genetics 5 (2005): 611-18. Print.
Stoneking, Mark. Hypervariable Sites in the mtDNA Control Region Are Mutational Hotspots. The American Journal of Human Genetics, Volume 67, Issue 4, Pages 1029-1032

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March 16, 2010 at 6:37 pm Leave a comment


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