Tracy Morton Sonneborn (October 19, 1905 – January 26, 1981) was an American biologist. His life's study was of the protozoan group Paramecium. Education Sonneborn attended the Baltimore City Public Schools and graduated from the Baltimore City College (high school) in 1922. As an adolescent, Sonneborn was interested in the humanities and considered becoming a rabbi. After taking a biology course taught by E. A. Andrews, his interest in literature was eclipsed by his interest in science. He earned a B.A. from Johns Hopkins University in 1925 and a Ph.D in 1928. His graduate work, supervised by Herbert S. Jennings, focused on the flatworm Stenostomum. Career Sonneborn spent 1928 and 1929 researching the ciliate Colpidium with Jennings as a National Research Council fellow. He remained at Hopkins until 1939, with appointments as research assistant, research associate, and associate. He was offered a faculty position at Indiana University, where he served as associate professor, professor (1943), distinguished service professor (1953), and distinguished service professor emeritus (1976). Sonneborn was elected to the United States National Academy of Sciences in 1946, the American Academy of Arts and Sciences in 1949, and the American Philosophical Society in 1952. Non-Mendelian inheritance In the late 1950s he conducted a series of experiments in his endeavours to discover what it is that mediates the synchronised movement of the paramecium's cilia. These minuscule hair-like projections enable the cell to 'swim'. They move together and paddle the cell through the water in which it lives. The paramecium is a single-cell organism, so has nothing remotely resembling a brain. Yet its cilia move together like dancers in a ballet. How is it that their movements are co-ordinated? Sonneborn surgically removed a small section of cell wall and replaced it rotated by 180 degrees. The cortex with the cilia in the replaced section continued to 'wave' in the same direction as they had before surgery, i.e. now in antiphase to the others. What was remarkable is that both daughters of paramecium on which this operation had been performed also showed the same trait of a reverse phase wave if the reversal overlapped the division plane. If the reversed cortex did not overlap the division plane then only one the progeny had the inverted sequence. Cortical inheritance has major implications for what occurs in human (or any fertilized) egg divisions. Sonneborn also showed the cytoplasmic inheritance of mitochondria and chloroplasts along with