Mendelian Inheritance of Adaptive Enzymes

Abstract

Saccharomycetes carlsbergensis and its haploid progeny adapt to melibiose fermentation after aerobic incubation in the presence of melibiose. S. cerevisiae and its haploid progeny lack the adaptive capacity. Data obtained from 175 progenies of the interspecific and of related hybrids are consistent with the view that S. carlsbergensis contains 2 pairs of dominant genes, each of which controls the production of a melibiose fermenting enzyme, and that S. cerevisiae is homozygous for the recessive allels. That 2 non-allelic loci control melibiose fermentation is indicated by the fact that despite regular segregation in backcrosses to the non-adaptive S. cerevisiae of 2 hybrid haplophase cultures, 2 out of 20 of the haplo-phase progeny of these hybrids fail to adapt to melibiose. Furthermore, in the backcross of one of these to S. carlsbergensis, one out of 7 of the progeny fail to react, while in the backcross to S. cerevisiae, none out of 6 react.