23andme reports over 700,000 individual genetic markers called SNPs (pronounced ‘snips’). SNP stands for ‘single nucleotide polymorphism.’ Which simply indicates that at some point in the genome there was a variation in one of the letters of DNA (A,T,C,G) from what was normally to be expected. For example a person might have a SNP with a ‘C’ at that location, whereas a ‘T’ would be what would normally be expected. SNPs are very common, as each of us are uniquely different genetically from each other. Many SNPs have been associated with certain risks (such as diseases or susceptibilities.)
Interpretation programs comb through the results and looks for these special SNPs. It then activates it own analytic machinery and reports back to the consultants any areas of special interest. This type of testing would have costs many tens of thousands of dollars as little as a few years ago; the fact that is available at such a reasonable cost is a testimony to the amazing developments in modern technology.