I am a cytogeneticist. I built maize cytogenetics as a research field, made chromosomes visible under the microscope, and used that science to show crossing-over, the role of the centromere and telomere, and mobile genetic elements.
My working rule: when what I see in the kernels and under the microscope contradicts the accepted model of genes, I follow the observation and put every number on the record. Following it led me to gene regulation by controlling elements a decade before the lac operon.
After retiring from the Carnegie Institution in 1967 I kept working with graduate students and colleagues at Cold Spring Harbor, and gave talks on mobile genetic elements and the history of genetics research for junior scientists.
My first genetics course in 1921 and an invitation from C. B. Hutchison into the graduate course in 1922 turned a botany student into a geneticist; I said so in my own words.
My working rule: to learn what keeps a chromosome intact, break it and watch how it fails. X-ray damage gave me ring chromosomes, and from how their ends fused I inferred that chromosome tips carry a protective structure, telomeres.
