“The Cornell Plantations is a place where time is kept not by the ticking of watches and clocks, but rather by the blooms and fruits of growing things.” The plants there not only reflect natural beauty, they also commemorate the quest for truth of Cornell’s pioneering geneticist and 1983 Nobel Prize winner, Barbara McClintock ’23.
“This is the place where Barbara used to work,” said Prof. Denise Costich, Cornell Biotech Center, a corn geneticist who has kept a well-preserved archive of McClintock’s old photos and newspaper clips. The land stretches over roughly 50 square meters now covered with grass, located just beyond the current corn field of CALS by Forest Home Dr. Few Cornellians know the historic significance of this field and the shed that bears McClintock’s name. It was here that McClintock, with other Cornell maize breeders, made a series of breakthroughs that would forever change genetics and modern biology.
From an early age, McClintock showed great interest in science and problem solving. For a while, financial difficulties and objections from her mother prevented McClintock from higher education. But this changed when her father came back from serving in World War I, and McClintock enrolled in Cornell University in 1919. At the time, Cornell’s Department of Plant Breeding did not accept female student as genetics majors, so she graduated with a B.S. in Agriculture in 1923.
Prior to the establishment of the plantations in 1944, the legendary corn field was called Emerson Garden. R. A. Emerson was the head of the Plant Breeding Department. He was considered a “spiritual father” of maize genetics. Under his guidance, Cornell housed a team of young scientists including Marcus Rhoades, George Beadle and Charles Burnham. In her second year of graduate studies, McClintock was hired by L. F. Randolph, a collaborator of Emerson, to assist him in studying correlation between maize chromosome number and linkage groups.
Cells store their DNA in convoluted coils called chromosomes. During typical cellular reproduction (mitosis), these chromosomes are completely copied before the cell splits into two identical copies. In meiosis, however, only half the genes are copied. Studying this process involved observing the cell during this process, and keeping track of these splitting chromosomes.
“However, at that time, even the base number for chromosomes in many corn varieties was still in question,” wrote Prof. Lee Kass, plant biology, in her co-authored work Mapping and Seeing: Barbara McClintock and the Linking of Genetics and Cytology in Maize Genetics.
By the spring of 1924, Randolf had applied a smear technique used to add color and definition to a cell, to clarify the chromosome numbers reported in previous results.
McClintock later improved this coloration effect by warming the sections after staining. Subsequent modifications allowed her to identify finer structures and patterns. These techniques contributed to her discovery of chromosome “crossing over”— where two chromosomes will come together and swap segments of DNA.
Although McClintock and Randolf successfully applied Bell’s method in studying a triploid corn plant in the Cornell stocks, their collaboration ended unhappily. McClintock was displeased that in their 1926 article Polyploidy in Zea mays L, Randolf’s name was placed first while she had done most of the work. “Additionally, Randolf was extremely careful, meticulous, and cautious. Mclintock was notably bright and liked to explore and modify new experiment techniques, which discomforted her employer,” wrote Kass.
In the 1930s, during the golden age of corn cytogenetics, Cornell’s Emerson Garden and the nearby shed were home to the corn researchers at Cornell. During the founding era of early genetic theory, corn and fruit flies were both used as the principle organisms in research. Corn was often the more challenging to work with, since only one generation could be grown a year compared to 25 generations of fruit flies.
“Corn people, at that time, jokingly claimed themselves to be better than the fruit fly people, because they have to show more shrewdness in selecting cross-breeding strains, any little mistake may cost them to wait for another year for the next generation.” said Prof. Margaret Smith, oplant breeding and genetics.
During this period, scores of high quality research papers consolidated Cornell’s leading position in corn cytogenetics, and from 1929 through 1931 Mclintock published nine papers, which included one of her most influential: A correlation of cytological and genetic crossing-over in Zea Mays, which she finished together with a graduate student, Harriet Creighton. Their simple experiment in corn provided the first evidence that genes on paired chromosomes would exchange places during meiosis. It confirmed the chromosome theory of inheritance for which Thomas Hunt Morgan would be awarded a Nobel Prize in 1933.
Mclintock’s work at Cornell was widely recognized and rewarded; she received a National Research Council Fellowship in 1931 and Guggenheim Fellowship in 1933.
After leaving Cornell, McClintock went on to win the 1983 Nobel Prize in Medicine and Physiology for the discovery of gene transposition— a phenomenon of gene “jumping” that can cause mutations in organisms.
“Barbara Mclintock’s work at Cornell was conducted at an area that is now known as Cornell Plantations. As the Plantations redesign the corn growing area in Emerson Garden, we want to celebrate and acknowledge her legacy,” said Raylene G. Ludgate, the Plantations Youth Education program poordinator. According to the director of the Plantations Donald A. Rakow, the rennovation will begin in January 2009 and end in June 2010. The area which was used by Cornell historic plant breeders will be highlighted, though specific approaches to doing this are still under design.
“Dr. Barbara Mclintock revolutionized our understanding of plant breeding and how genes passed from one generation to another using corn as her model plant,” said Rakow. “All subsequent understanding in the plant genetic field has been based on the findings she made about gene transference.”