A modest Midwesterner who became one of the most influential geneticists of the first half of the 20th century, William E. Castle spent his career at Harvard and the University of California working on patterns of inheritance in mice, horses, and a variety of other mammalian taxa. An early proponent of Mendelian theory, Castle was director of the Bussey Institution at Harvard for almost thirty years, helping to train a number of important geneticists. The Castle Papers contain one linear foot of correspondence dating primarily from the period after Castle's "retirement" to Berkeley in 1936 until his death in 1962, dealing almost exclusively with his research on horse breeding and the inheritance of coat coloration in horses. Castle's correspondence with his former student L. C. Dunn is an exception, focusing on mouse genetics and ranging to a variety of topics from the conduct of scientific research during the Second World War to Castle's interests in the early history of genetics.

L.C. Dunn was one of the most significant figures in the emerging field of developmental genetics in the 20th century. His T-locus work with the mouse established a number of important genetic principles, including ideas of gene interaction, the distribution of alleles in wild populations, and the factors that influence fertility. He wrote an important textbook of genetics, Principles of Genetics (1925), in collaboration with Sinnott (and later Dobzhansky); other significant books authored or co-authored by him include Heredity, Race and Society (1946), and A Short History of Genetics (1965). He worked in poultry genetics for eight years at the Agricultural Experiment Station in Storrs, CT, from 1920-1928. The remainder of his career was spent at Columbia University, where he worked with rats, mice, and fruit flies, and proved himself to be an inspiring teacher as well. His interest in international scientific collaboration led him to establish ties to Soviet scientists, and to help relocate refugee scientists during World War II. He remained active in his profession to the end of his life. This collection includes correspondence, reports, notebooks, lectures, and photographs. It is a rich collection, documenting the development of American genetics as well as Dunn's interests in humanitarian efforts and international affairs. There is significant material relating to American-U.S.S.R. contacts, particularly in the files on the American-Soviet Friendship Council and the American-Soviet Science Society. There is much, as well, on the impact of the Lysenko controversy in the U. S. Dunn's interest in European scientists can also be seen in the sizable amount of material on the Emergency Committee in Aid of Displaced German Scholars. Material relating to the Kilgore and Magnusson bills for the support of science (predecessors to the NSF) are also in the collection. Of note are data on the following: National Research Council Committee on Experimental Animals and Plants; research on the population study of the Jewish community in Rome; and Columbia University. There is much in the correspondence concerning Drosophila, poultry genetics, and other such topics; Walter Landauer is Dunn's major correspondent.