Induction of sporulation in developmental mutants of Bacillus subtilis.

Summary Eight alleles of spineless-aristapedia (ss^a) were analysed for penetrance and expressivity at 18° C and 25° C. All alleles are recessive and none exhibits a maternal effect. Both ss^a40a and ss^aB are temperature sensitive with a higher penetrance at 18° C than 25° C. ss^aUCI, ss^ak, ss^a, ss^ax and ss^a are viable alleles with variable penetrance and expressivity whereas ss^aCam is a lethal allele. All mutants were tested as hemizygotes using the Df(3R) bxd¹⁰⁰ deletion. The viable alleles showed a more extreme penetrance and expressivity when hemizygous, several becoming lethal near eclosion. Each of the eight alleles was examined in heterozygous combinations with each of the others. The lethal allele ss^aCam was viable in combination with all other alleles. The temperature sensitivity (t.s.) of ss^aB and ss^a40a when heterozygous with the non-t.s. alleles was variable; some combinations were t.s. with respect to penetrance and others with respect to expressivity, whilst some heterozygotes completely lost their sensitivity to temperature.It seems, therefore, that various aspects of the spineless-aristapedia phenotype, such as the temperature sensitivity, can be separated from the expressivity and penetrance in certain allelic combinations. This suggests a very complex gene function which is, however, experimentally separable into its components.