Robert G. McKinnell (e-mail: firstname.lastname@example.org) is a professor of Genetics and Cell Biology at the University of Minnesota, Saint Paul, MN 55108-1095. He is the author of Cloning: Nuclear Transplantation in Amphibia (1978) and Cloning of Frogs, Mice and Other Animals (1985) and the 1998 recipient of the Prince Hitachi Prize in Comparative Oncology, awarded by the Japanese Foundation for Cancer Research. Marie A. Di Berardino (e-mail: email@example.com) is a professor emerita of Biochemistry at MCP Hahnemann University, Philadelphia, PA 19129. She is the author of Genomic Potential of Differentiated Cells (1997) and the 1996 recipient of the Jean Brachet Memorial Award, given by the International Society of Differentiation, Inc.