Mendelian Inheritance of Genes Affecting Vitamin-Synthesizing Ability in Saccharomyces

Pedigrees describing both Mendelian and non-Mendelian inheritance of the ability to ferment carbohydrates in Saccbaromyces have been reported by us (Lindegren and Lindegren,, '47). Genes controlling the fermentation of galactose, maltose, or, melibiose are transmitted in a regular Mendelian manner in some pedigrees, and in a non-Mendelian manner in others. Present indications are that this is due to the gene-to-gene transfer of some essential gene-component controlling fermentation. This phenomenon complicated the problem of genetical analysis of yeasts until regular Mendelian pedigrees were available. The diagnosis of the fermentative ability of any selected culture is clear-cut, no difficulty being experienced in distinguishing a fermenter from a non-fermenter. In the present pedigree the fermentation of sugar is usually complete after 48 hours; the negatives do not ferment when held for three weeks. When regularly segregating pedigrees became available, the problem of genetical analysis of fermentative ability was capable of an uncomplicated solution. Burkholder's medium (Lindegren and Raut, '47) is an excellent diagnostic medium for distinguishing pantothenate "synthesizers" from "nonsynthesizers," because a so-called nonsynthesizer grows rapidly in this meduim containing pantothenate, but requires weeks or months to pr'oduce growth in its absence. 'However, genes affecting vitamin synthesis are apparently transmitted in some pedigrees in a non-Mendelian way similar to that displayed by genes controlling fermentation. The first pedigree on the inheritance of "vitamin-synthesizing" ability in Saccharoxmyces (Li~ndegren, '45) failed not only to reveal regular Mendelian inheritance of this ability but also of genes controlling the fermentation of carbohydrates. In our selected inbred strains, the ability to ferment galactose and maltose is transmitted in a regular Mendelian manner, and the present paper shows that genes affecting the synthesis of paraminobenzoic acid, pantothenate, pyridoxine, and thiamin are transmitted with corresponding regularity. These genes are described as "affecting" iather than "controlling" the synthesis of vitamins, because we have not discovered any absolute deficiencies in yeasts. Lindegren and Raut have shown that a so-called nonsynthesizer of pantothenate eventually will grow in a medium without the addition of pantothenate, although some cultures do not begin growth until they have stood in the tubes for nearly a month.