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SUMMARYIn order to investigate the importance of the nuclear genotype during morphogenesis of the cortex inParamecium aurelia, a search was made for conditional and unconditional mutants affecting cell shape. Ten different mutants were readily recovered following mutagenesis withN-methyl-N-nitro-N-nitrosoguanidine on stock 51s of syngen 4. The detailed pattern of surface units remained unchanged in these mutants but each one can be described as resembling a normal cell twisted about its long axis. Nine of the mutants complement each other and show no linkage. The remaining mutant, a ‘chain former’, has conditional expression, and is only recognizable at 35 °C. The penetrance of this mutant is affected by the food organism used. The conditional mutant also interacts with seven of the other mutants in pairwise homozygous combinations so that in these genotypes it can be classified after growth at 25 °C. The mutants are discussed in relation to the search for genie effects on the cortical pattern.

The Organization of Heredity . By Kenneth R. Lewis & Bernard John. Pp. ix + 241. (Arnold: London, September 1970.) 70s boards; 35s paper.