and later Ham’s F12 media, which are still widely used. He established and characterized the Chinese hamster ovary cell line K1 (CHO-K1), which remains a mainstay of modern mammalian cell genetics and is widely used in academic labs and in many biotechnology companies because of its favorable growth characteristics and ease of use for many different kinds of experiments (Puck, 1985). These innovations were critical for the success of somatic cell genetics.

Shortly after devising the single-cell plating technique, Ted and his colleagues determined the mean lethal dose of X irradiation required to kill mammalian cells (1956,2). This experiment is widely recognized as one that revolutionized the field of radiation biology. It is also recognized as having a revolutionary effect on the use of radiation to treat cancer. Another early contribution involved the definitive proof that humans have 46 chromosomes. Clearly this was first shown by Tjio and Levan, but their results were not easily accepted (Tjio and Levan, 1956); for example, in 1958 a suggestion was made that humans could have 46, 47, or 48 chromosomes, and that Caucasians and Japanese might differ in this regard (Kodani, 1958). Ted’s immediate recognition of the outstanding nature of Tjio and Levan’s cytogenetic work led him to invite Tjio to join the laboratory, where they made important contributions firmly demonstrating that 46 is indeed the correct number of human chromosomes (1958,1). He organized a seminal meeting in 1960 in Denver that established the Denver system of chromosome classification that is the basis for the methods still used today (1960,2).

Ted and his colleagues developed the first practical method for isolating auxotrophic mutants of CHO-K1 cells (1967,2; 1968). His laboratory was one of the first to use somatic cell hybridization to map genes onto human chromosomes and the first to identify different complementation groups among auxotrophic mutants with the same