American Botanist 1909-
Harriet Baldwin Creighton is a geneticist who helped prove that genes are located on chromosomes. She was born in Delevan, Illinois, on June 27, 1909. She attended Wellesley College in Massachusetts and received her Bachelor of Arts degree in 1929. That year she matriculated at Cornell University as a botany graduate student and a laboratory assistant in botany. At that time Barbara McClintock, who later became a top American plant geneticist and Nobel Prize winner in medicine in 1983, was an instructor at Cornell. The two women immediately became friends and began working together on an important genetic problem: since the beginning of the twentieth century, cytologists theorized that chromosomes carried and exchanged genetic information to produce new combinations of physical traits, but cytological evidence to prove their hypothesis was lacking.
McClintock had bred a special strain of corn (Zea mays ) with a ninth chromosome that produced a waxy, purple kernel. In the spring of 1930, Creighton and McClintock planted the kernels from this strain. That summer they fertilized the silks with pollen from a plant of the same strain that did not have either waxy or purple kernels. Once the ears were harvested in the fall, Creighton and McClintock found that some of the kernels were waxy and purple and others had inherited one trait or the other—either waxy or purple—but not both, indicating that the two genes had become separated.
When Creighton and McClintock examined the chromosomes of the new kernels under a microscope they saw that the chromosomes had crossed-over, or exchanged segments. They thus proved that genes for physical traits are carried on chromosomes. This process is extremely complex, and cytologists had been working to understand it for more than thirty years. Creighton and McClintock were the first to provide cytological evidence in plants that proved corresponding segments of genetic material on the chromatids of homologous chromosomes are able to cross over during meiosis. They published their remarkable findings in the Proceedings of the National Academy of Sciences, "A Correlation of Cytological and Genetical Crossing-over in Zea mays."
Creighton completed her Ph.D. in botany at Cornell in 1933. She went on to teach at Connecticut College as assistant professor of botany in 1934 where she remained for the next six years. In 1940 she accepted a position as an associate professor of botany at Wellesley College in Massachusetts. Creighton's professional career is graced with many distinguished honors. She was twice a Fulbright Lecturer, once in genetics and plant physiology at the University of Western Australia and the University of Adelaide in 1952 and 1953, and again in genetics at the University of San Antonio Abad, Peru in 1959 and 1960. Creighton was the first female secretary of the Botanical Society of America (1950-54); she also served as vice president in 1955 and president in 1956. In addition Creighton was a fellow of the American Association for the Advancement of Science (AAAS) where she served as vice president of the Botanical Sciences Section in 1964. Throughout her professional career, she continued to work in the field of plant genetics; much of her research focused on problems of heredity in corn, but her later research sought to investigate the "mad begonia," Begonia phyllomania, with its strange growth patterns, which Creighton believed might hold important clues for cancer researchers. She retired from Wellesley College in 1974.
see also Corn; McClintock, Barbara.
Mary Anne Andrei
Creighton, H. B., and B. McClintock. "A Correlation of Cytological and Genetical Crossing-Over in Zea mays." Proceedings of the National Academy of Science, 17 (1931): 492-97.