Maintenance and Increase of a Genetic Character by a Substrate-Cytoplasmic Interaction in the Absence of the Specific Gene

Abstract

The effect of melibiose on the inheritance of the ability to ferment this sugar has been studied in Saccharomyces hybrids heterozygous for a gene controlling adaptation to melibiose. Each 4-spored ascus from the diploid cell yielded 2 adaptable and 2 unadaptable haplophase cultures in the absence of melibiose. However, identical heterozygotes treated with melibiose yielded 4 adaptable spores from each ascus. All 4 haploids and the clones derived from them can maintain the ability indefinitely but when melibiose is removed only 2 out of 4 can readapt to its fermentation. These results are explained in terms of transfer of the trait from one generation to the next by enzyme molecules contained in the cytoplasm, melibiose might obscure the gene mechanism if it were the specific substrate for such an enzyme. Alternative genetic explanations are considered to be less plausible.