Home DNA tests make quite a few claims, including assisting one in determining their potential medical history and future. Are you predisposed to developing Alzheimer or MS? Do you carry certain genes that increase your risk of certain types of cancers? These are very valid questions that some might be very interested in answering, but can home DNA tests accurately provide those answers? The simple answer is that they cannot. It even states as much on many of these products in the fine print that warns against using the tests for medical advice. This could have simply started as a clause that the company's lawyers demand be added (so as to avoid lawsuits), but a recent study published in the journal Nature supports this claim that these tests are not medically viable. In their study they concluded that 40% of the test results were inaccurate, meaning people were receiving false data about their health. Those who believe this information, particularly the false information, could undergo unnecessary medical treatment (e.g. mastectomies to avoid breast cancer) or forgo regular check ups because they believe they are not at risk (e.g. skipping mammograms, which by the way do not hurt, so please go do them). Therefore these tests should not be considered medically sound advice when it comes to your health, and one should always consult a medical professional for matters concerning health and wellness.
Another favored purpose of home DNA tests is to determine one's ancestry. At least one company has come out with a series of commercials about this, and one even demonstrated how a user discovered that his family's ancestry was not German but instead Scottish, leading him to give up highland dancing for more "appropriate" Bavarian customs (which, by the way, are not accurate in the commercial). But can these tests actually provide an individual with this information accurately? Again, the answer is no.
The reasons for why your home DNA tests cannot provide accurate ancestry information are a bit more complex, however. First and foremost, race and ethnicity are socially constructed concepts and not biologically sound. There is no one strand of DNA that makes up one's racial or ethnic classification. In fact, there are several DNA strands that make up the various (and ever changing!) biological traits associated with race and ethnicity: e.g. hair texture, eye shape, nose shape, butt shape, skin color, etc. Several of these traits can be found in various "racial" groups (as noted by a colleague of mine who asked why there were more white women demonstrating the "characteristic" black girl booty [altered the quote to protect identity of my source], my girlfriend in graduate school who claimed to have a "big black ass" when she was of "Caucasian" and "Middle Eastern" descent, and my sister, Oma, dear friend and his daughter all of whom have the "Asian" almond shaped eyes, although none are of Asian but instead all of Eastern European descent). So first and foremost it must be stressed that the ability of any of these tests to trace one's ancestry is inherently flawed because biologically there is more genetic diversity within groups than outside of them, so tracing any individual back to specific "racial" or "ethnic" groups is bogus.
Second, the nature of genetic inheritance makes it difficult to trace descent as you move further back through the generations. Your genetic make up is largely determined by your parents' genetics. You could receive the majority of genetic traits from either parent, it could be equal, or it could be any type of proportion (e.g. 60/40; 29/71; 38/62, etc.). There is no consistency, hence why you could have two siblings that look very similar or not at all alike. Your parents' genetics are based on what their parents provided them, so in a small way your grandparents are contributing to your genetic makeup. This is why you may have your grandmother's eyes (as is the case with my sister) or your grandfather's chin (e.g. one of my cousins). Each generation previous to your parents is providing less and less genetically to you, as well as to any potential offspring you may have. Therefore, if we actually attempt to trace one's genetics back to say the great-great-great-great grandparents there are going to be some issues because their DNA is going to look very different from the DNA in their modern descendants.
Furthermore, home DNA testing companies actually only test no more than 1% of all of the DNA you provide them, and they sometimes only focus on the mother or father's contribution. This means that you are already losing out on a lot. It gets even worse when you understand what groups they are using for comparison-modern groups. Therefore when you get the results back stating that you are X% this specific group (e.g. Central American) the results say that your DNA most closely resembles modern people of that group than past people of those groups. If we look at the social/cultural history of Central American populations (e.g. colonialism, immigration, slavery, genocide, etc.) it should be of no surprise that modern populations are going to look biologically/genetically different from their ancestral populations.
As stated in the very beginning this post is not meant to stop you from taking these tests. If you really want to pursue them then go for it. In fact, they have been beneficial in some ways, specifically in making people realize that we are more similar than we are different. There are, however, serious cautionary notes that must be realized prior to taking these tests. They do not and should not replace advice and information provided by a trained medical professional, and they do not provide you with accurate information about your family's ancestry, just who you appear to be most similar to based on today's genetic diversity. They should be used for fun, and if it's fun you are looking for then go for it.
Bibliography
Burley, Ron. 2011. “A Case of Mistaken Ancestry.” AARP.org
