Parasexual genetic analysis of the cellular slime mold Dictyostelium discoideum A3 [Fungi]

• Published in: Genetics (Austin) 1975-08, Vol.80 (4), p.715-731
• Main Authors: Rothman, F.G, Alexander, E.T
• Format: Article
• Language: English
• Subjects: Acriflavine - pharmacology; Dictyostelium - drug effects; Drug Resistance; Genetic Linkage; Genotype; Haploidy; Investigations; Methanol - pharmacology; Mutation; Myxomycetes; Phenotype; Recombination, Genetic; Sex
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/80.4.715

Haploid strain A3 of the cellular slime mold Dictyostelium discoideum is valuable for biochemical studies because it is capable of axenic growth. Mutants of A3 temperature-sensitive for growth and resistant to the drugs cycloheximide, acriflavin, or methanol were isolated.--Heterozygous diploid recombinants, formed at low frequency by cell and nuclear fusion, were isolated by selecting temperature-resistant progeny of mixed cultures of two nonallelic temperature-sensitive haploids (LOOMIS 1969). Each drug-resistant mutation was found to be recessive. Two independently isolated methanol-resistant mutants were in one complementation group.--Diploids of A3 heterozygous for drug resistance formed drug-resistant segregants with a frequency of approximately 10(-4). Segregants selected for resistance to a single drug were either haploid or diploid; the fraction which was haploid varied from 0.11 to 0.86, depending on the selected marker. Segregants selected for resistance to two or three drugs were almost all haploid.--Using this parasexual cycle of diploid formation and haploidization, linkage of these temperature-sensitive and drug-resistance mutations to each other and to mutations studied by KATZ and SUSSMAN (1972) and by WILLIAMS, KESSIN and Newell (1974b) was analyzed. The methanol-resistant mutants were found to be partially resistant to acriflavin, and unlinked to the mutant selected for acriflavin resistance, which was methanol-sensitive. Of the expected seven linkage groups in D. discoideum, five, and a possible sixth, have been marked.--Linkage analysis of a mutant abnormal in morphogenesis showed that its phenotype results from two unlinked chromosomal mutations.