You’ve no doubt seen the advertisements for DNA testing services that offer to test your DNA to find out your entire genetic history. Ancestry.com and 23andMe are the most famous of the DNA testing companies. And people love these services: over 26 million DNA tests have been performed across all the major companies. The tests are fairly affordable for most people too: the retail cost of these tests are about $50 to $140 per testing kit. And less if you use an Ancestry DNA coupon on your order. But how does the science behind these services work? And are the …