1. Curriculum in Genetics and Molecular Biology (C.A.B., M.E.L., S.J.L.), Department of Biology (S.K.O., I.C., S.J.L.), and Biological and Biomedical Sciences Program (C.E.W.), University of North Carolina, Chapel Hill, North Carolina 27599; Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908 (M.J.D.)