<Tr> <Th> Thesis </Th> <Td> A Cytological and Genetical Study of Triploid Maize (1927) </Td> </Tr> <Tr> <Th_colspan="2"> Signature </Th> </Tr> <P> Barbara McClintock (June 16, 1902--September 2, 1992) was an American scientist and cytogeneticist who was awarded the 1983 Nobel Prize in Physiology or Medicine . McClintock received her PhD in botany from Cornell University in 1927 . There she started her career as the leader in the development of maize cytogenetics, the focus of her research for the rest of her life . From the late 1920s, McClintock studied chromosomes and how they change during reproduction in maize . She developed the technique for visualizing maize chromosomes and used microscopic analysis to demonstrate many fundamental genetic ideas . One of those ideas was the notion of genetic recombination by crossing - over during meiosis--a mechanism by which chromosomes exchange information . She produced the first genetic map for maize, linking regions of the chromosome to physical traits . She demonstrated the role of the telomere and centromere, regions of the chromosome that are important in the conservation of genetic information . She was recognized among the best in the field, awarded prestigious fellowships, and elected a member of the National Academy of Sciences in 1944 . </P> <P> During the 1940s and 1950s, McClintock discovered transposition and used it to demonstrate that genes are responsible for turning physical characteristics on and off . She developed theories to explain the suppression and expression of genetic information from one generation of maize plants to the next . Due to skepticism of her research and its implications, she stopped publishing her data in 1953 . </P>

Who was awarded the nobel prize for the discovery that genes can change position on chromosomes