Characterization of Dominant Resistance to Cobalt Chloride in DICTYOSTELIUM DISCOIDEUM and Its Use in Parasexual Genetic Analysis.

Strains of Dictyostelium discoideum resistant to cobaltous chloride have been isolated at a frequency of approximately 10(-6). The resistant strains have one of three phenotypes, recessive to wild type, dominant to wild type and dominant to wild type but requiring the presence of cobaltous chloride to maintain resistance. Strains carrying a dominant cobaltous chloride resistance mutation and a recessive growth temperature-sensitive mutation can be mixed with wild-type haploid lines and then subjected to selection so that only diploid lines survive. Differential sensitivity to cycloheximide has also been observed. Hypersensitivity to cycloheximide in combination with dominant cobaltous chloride resistance provides a means of selecting diploids without the use of temperature-sensitive mutations.