Passage V

Barbara McClintock and the Genetics of Maize

As a leader in the field of genetics, Barbara McClintock of human genes made significant steps in unraveling the mysteries. When she began studies in the 1920s, scientists had only recently began to consider genetics a field of study and accept the research of Gregor Mendel (1822-J884). (62) His theory stated that plants resembled their "parents" in a predictable manner based on laws of inheritance. However, McClintock's research pushed the field of genetics beyond Mendel's principles.

McClintock believed maize (corn) was idealistically a plant to study because each ear had hundreds of kernels for each with a different set of chromosomes. The first to perfect a staining technique for distinguishing the individual chromosomes of maize. McClintock studied the way genes were arranged on these chromosomes. By 1951, she had studied many generations of maize, noting the locations of groups of genes as the plants reproduced.

McClintock found that some of the maize kernels were striped or spotted rather, then the uniform color found in the parent plants. For example, these findings were in marked contrast to Mendel's work, which had concluded that the kernel color of offspring could be predicted from the combination of genes inherited from the parent plants. In the multicolored kernels, McClintock discovered that specialized genes, later called transposons, were changing positions on and between the chromosomes. These changes caused a deviation from the kernel color of the maize that would have been anticipated by scientists. McClintock named this genetic phenomenon transposition.

McClintock's work was far ahead of the other genetic research of her time. It took the scientific community over thirty years to understand and publicly recognize her discoveries. In other scientific fields, the concept of transposition may had wide-ranging applications, and in the development of medical treatments for bacterial infections and cancer. After the importance of her research gained appreciation for its value, she was awarded the Nobel Prize in Physiology or Medicine in 1983.