Barbara McClintock Maize Chromosome Slides Collection

Nearly all of these slides and notes were made by Dr. Barbara McClintock between the years1925 and 1944. There are 96 slides of maize material, 3 slides of Vicia Faba (common bean) roots, and 36 slides of Neurospora. Along with the slides are McClintock’s handwritten “camera lucida” drawings of chromosome images on the slides and la handwritten letter addressed to Dr. McClintock. In all cases [looked at in 2025], the stained maize chromosomes are still visible under the microscope. Frances Janes Clark, who conducted research with Dr. McClintock during the summers of 1937-1939, was accompanied by a letter from FJC to BM dated Tuesday, April 30 (1940).

The content of the collection contains a variety of maize chromosome spreads from plants containing translocations, ring and B chromosomes, and a maize-teosinte hybrid. The original plant material was labeled with McClintock, Rhoades, Stadler, Anderson and Burnham pedigree numbers. Also included is a set of fixed Neurospora spreads which undoubtedly came from McClintock’s study of Neurospora during or soon after her visit to George Beadle at Stanford University (1944).

With relevance to the discovery of transposable elements, slides containing mitotic spreads of leaf tissue show dicentric bridges demonstrating the “chromosome type” of the Breakage-Fusion-Bridge cycle. Additionally, one slide contains a meiotic pachytene image of a heterozygous chromosome 9 deletion; A chromosome configuration used in the induction of broken chromosomes. Controlling elements were discovered from plants that underwent the chromosome and chromatid type BFB cycles.