Courtesy Carnegie Institution for Science Administrative Archives
Imagine looking into a small world of genetic elements interacting intricately with each other, where genes give rise to complex proteins and chromosomes dance together as they replicate. For cytogeneticist Barbara McClintock, her extensive research with maize cytogenetics allowed her to dive intimately into a molecular world. As one of the most distinguished scientists of the previous century, McClintock’s discoveries brought new insights into the world of genetics as she led a life of historical and scientific firsts.
Barbara McClintock was born on June 16, 1902 as the third child in a family of four children. Initially given the name “Eleanor”, she later changed her name to “Barbara” because she believed her birth name was too feminine and delicate. As a child, she was independent and solitary. Her love of science began in high school, and in 1919 she began her studies at Cornell’s College of Agriculture. Her scientific interests narrowed down to genetics when she took her first botany class in 1921, later receiving her B.S. in 1923 and her P.hD. in 1927, both in botany, perhaps because Cornell did not allow women to major in Genetics at the time. Despite this, she became an influential member of a small yet outsized group by reputation that studied maize cytogenetics.
McClintock’s early work was nothing short of revolutionary. Between 1929 and 1935, she was responsible for ten out of seventeen advancements made by Cornell scientists in the field of maize cytogenetics. She developed a groundbreaking methodology for visualizing maize chromosomes, showing their morphology and linking regions from each chromosome to physical traits. In 1931, McClintock proved the correlation between the recombination of genetic traits and the crossing-over of sister chromatids and homologous chromosomes during meiosis. This was the first physical evidence of crossing-over, which previously only existed in theory. In 1933, she observed the “stickiness” of chromosomes without end parts and hypothesized the existence of a special structure for chromosome stability -- an early prediction of telomeres. McClintock also observed the rejoining of chromosomes within irradiated maize cells, leading to the discovery of the breakage–fusion–bridge cycle (BFB). The BFB is known today as a key mechanism of genetic instability and large-scale mutation, and remains an area of interest for cancer research.
McClintock worked at the University of Missouri for most of the 1930’s, but eventually grew dissatisfied with her position. Although she was offered security in the form of potential tenure at Missouri, her freedom to conduct research was restricted by university responsibilities (teaching, committee work, and publication deadlines). She was treated differently from her male colleagues, often finding herself being excluded from faculty meetings and was kept in the dark about positions at other institutions. In addition, her continued employment depended on the presence of geneticist Lewis Stadler, who had created McClintock’s position at the university.
McClintock decided to leave for a better position and eventually settled to work at the Carnegie Institution of Washington’s Cold Spring Harbor Laboratory, where some of her most impressive research was performed. During the 1940’s and 1950’s, McClintock investigated the mosaic patterns of maize seeds. She discovered loci that could transpose on the chromosome and consequently affect the color of maize kernels. Later dubbing these loci as “controlling elements”, McClintock hypothesized that transposition and gene regulation could explain the differentiation of cells sharing an identical genome. However, her findings were arguably ahead of her time. Many scientists were sceptical of her work, and did not become widely accepted until the 1960’s and 1970’s.
Throughout her impressive career, McClintock received multiple awards and recognition for her work. After officially retiring from the Carnegie Institution in 1967, she was made a Distinguished Service Member and continued to work, typical of many luminary Carnegie scientists. In 1970, she became the first woman to receive the National Medal of Science. In addition, she was the first recipient of the MacArthur Foundation Grant (now known as the “genius” grant), awarded in 1981 for her talent and accomplishments. Her most notable award was the Nobel Prize in Physiology or Medicine, awarded to her in 1983 for her work on transposable elements. She was the first woman to win that award unshared, and the first American woman to win any Nobel Prize unshared.
McClintock eventually passed away on September 2, 1992, having lived an incredible 90 years full of discovery. As a woman who changed the way we understand genetics, her legacy is invaluable.
--by David Hoang (2019), Carnegie Summer Intern in the Rhee lab