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John Littlefield Dies

John Littlefield, a pediatrician and geneticist at Johns Hopkins University School of Medicine, has died, the Baltimore Sun reports. He was 91.

During his career, Littlefield worked with Francis Crick and James Watson — he was their research assistant for a time — and was involved in work that determined the role of the ribosome in protein synthesis. In addition, Littlefield developed a way to isolate hybrid cells, an approach that the Sun notes has since been used in genetic mapping. In addition, Littlefield helped pioneer amniocentesis as a way of diagnosing prenatal genetic disorders.

This meant that families susceptible to genetic disorders "who normally might have avoided having children could now safely screen for disorders and make better informed choices about family planning," wrote Elizabeth Littlefield, John Littlefield's daughter, in a profile of her father.

After retiring in 1992, Littlefield continued to conduct research and was part of John Gearhart's team at Hopkins that identified, isolated, and grew human embryonic stem cells, the Sun adds.