Mail your spit to a stranger and learn more about yourself. It sounds crazy (and a little gross), but thanks to Anne Wojcicki's 23andMe, DNA sequencing (the name refers to the number of pairs of chromosomes in humans) is available to anyone with $399 and enough saliva to fill a test tube. "We were incredibly frustrated," says Wojcicki, who launched the Silicon Valley start-up three years ago. "We'd like to see medicine significantly more personalized, but that won't happen unless we all become active participants." The goal is "democratized genetics," equal access for everyone to the secrets of their biological makeup (genome scanning can offer insights into everything from ancestry to disease predisposition). Speaking of DNA, Wojcicki, who married Google's Sergey Brin in 2007, borrowed a little from Flickr and Facebook, building 23andMe as a social network, on which guys can track male pattern baldness on their mother's side of the family or swap stories with other sufferers. "It's no longer about going to your doctor—we want people to communicate," she says. "If we give individuals information and form communities around that, we can revolutionize and dramatically accelerate the pace of research."

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