The H1N1 swine flu virus kills some people, while others don't get very sick at all. A genetic variation offers one clue. Centre For Infections/Health Pro/Science Photo Library/Getty Images hide caption

itoggle caption Centre For Infections/Health Pro/Science Photo Library/Getty Images

MaryAnn Anselmo has started to sing again after recovering from brain surgery and having successful treatment with a drug that targeted a mutation in her tumor cells. Dave Gershgorn/WNYC hide caption

itoggle caption Dave Gershgorn/WNYC

A simulation from the Neitz lab of what colorblindness looks like, with normal color vision on the left and red-green colorblindness on the right. Courtesy of Neitz Laboratory hide caption

itoggle caption Courtesy of Neitz Laboratory

Both James Eversull (left) and Pat Patchell were treated with experimental chemotherapy and radiation for leukemia as children in the 1960s. Together, they're now some of the country's oldest leukemia survivors.. Courtesy of James Eversull; Courtesy of Pat Patchell hide caption

itoggle caption Courtesy of James Eversull; Courtesy of Pat Patchell

Grey lines connecting health care workers (marked with "+") and patients represent contacts between them. The red figures are carriers of MRSA. Obadia et al./PLOS Computational Biology hide caption

itoggle caption Obadia et al./PLOS Computational Biology

A nurse in 1938 checks the amount of insulin in a needle. For many decades, the only insulin available to people with diabetes came from the pancreases of cattle or pigs. Insulin from animals is still available outside the U.S. — and cheaper than a recombinant DNA version. Bettmann/Corbis hide caption

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Feces contain digested food residue and a wide variety of microorganisms, mostly bacteria, that are adapted to life in the intestines. The gases the microbes produce could help doctors and scientists track and understand changes related to health. Scimat Scimat/Photo Researchers/Getty Images hide caption

itoggle caption Scimat Scimat/Photo Researchers/Getty Images