Seeing patterns: Models, visual evidence and pictorial communication in the work of Barbara McClintock

Barbara McClintock won the Nobel Prize in 1983 for her discovery of mobile genetic elements. Her Nobel work began in 1944, and by 1950 McClintock bega n presenting her work on "controlling elements.'' McClintock performed her studies through the use of controlled breeding experiments with known mutan t stocks, and read the action of controlling elements (transposons) in visi ble patterns of pigment and starch distribution. She taught close colleague s to "read'' the patterns in her maize kernels, "seeing'' pigment and starc h genes turning on and off. McClintock illustrated her talks and papers on controlling elements or transposons with photographs of the spotted and str eaked maize kernels which were both her evidence and the key to her explana tions. Transposon action could be read in the patterns by the initiated, bu t those without step by step instruction by McClintock or experience in mai ze often found her presentations confusing. The photographs she displayed b ecame both McClintock's means of communication, and a barrier to successful presentation of her results. The photographs also had a second and more su btle effect. As images of patterns arrived at through growth and developmen t of the kernel, they highlight what McClintock believed to be the developm ental consequences of transposition, which in McClintock's view was her cen tral contribution, over the mechanism of transposition, for which she was e ventually recognized by others. Scientific activities are extremely visual, both at the sites of investigation and in communication through drawings, photographs, and movies. Those visual messages deserve greater scrutiny by historians of science.