Thanks to companies like 23andMe and AncestryDNA, personal DNA testing is hot. For a couple hundred dollars or less, you can find out where your ancestors came from, in case you need to swap out your lederhosen for a kilt, as in one memorable ad. Most of us recall when DNA sequencing was cutting edge technology, and took years and millions of dollars to accomplish. How do these companies do it for so many people? Well, for one thing, they don't map all your DNA.
2. THE KITS LOOK FOR GENETIC VARIATIONS CALLED SINGLE NUCLEOTIDE POLYMORPHISMS.
After extracting DNA from your cheek swab or saliva sample, DNA testing companies search your DNA for certain genetic variants. The building blocks of DNA are chemical bases called nucleotides, which come in four varieties—A, T, C, and G (adenine, thymine, cytosine, and guanine, respectively). We have 3 billion pairs of these bases, so 6 billion letters in all, strung together in a sequence. Altogether, this genetic information is called your genome.
DNA testing companies determine which of the four letters is present at many locations in your genome. Much of the sequence is shared among humans, so the companies focus on specific letters that vary from person to person, known as single nucleotide polymorphisms (SNPs). Many SNPs have some biological relevance. For example, having one variant of a specific SNP near the gene OCA2, which codes for a protein believed to be involved in producing the dark pigment melanin, makes it much more likely you’ll have blue or green eyes. Other traits and even some diseases are also associated with certain SNPs, some more strongly than others.
That's one of the many ways that commercial DNA testing stands on the shoulders of earlier, more expensive research. Read more facts about personal DNA tests at Mental Floss.
(Image credit: Flickr user University of Michigan School for Environment and Sustainability)