27-15 THE YEAST CELL 



GENE -DOSAGE AND GENE -PRODUCT 



Conclusive evidence that genes control the composition of the 

 cytoplasm both qualitatively and quantitatively (and, therefore, do 

 not produce autonomous plasmagenes) is derived from studies on 

 the effect.of gene -dosage on phenotype. Mangelsdorf and Fraps 

 (1931) showed that the concentration of carotinoids (and vitamin A) 

 bore a linear relation to the dosage of genes controlling yellow 

 color. Stern (1943) showed that one dose of the ci gene produced 

 a very abnormal wing, two doses a less abnormal wing, and three 

 doses a nearly normal wing. A closer approach to normal was at- 

 tained with each added gene. The same conclusion can be drawn 

 from both observations: Since quantitative measurement of the 

 phenotype bears a direct relation to gene -dosage, the gene pro- 

 duces a product which is incapable of autonomous multiplication 

 in the cytoplasm. Each molecule of gene -specific substance in 

 the cytoplasm arises from the production of an equivalent 

 (specificity-conferring) molecule by the gene. Therefore, sub- 

 strate induces the production of an enzyme by acting on the gene 

 and not by a plasmagene -substrate interaction. The gene apparent- 

 ly controls both the quantitative and the qualitative composition 

 of the cytoplasm subject (1) to modifications imposed by changes 

 in gene^product to gene equilibria and (2) to the presence in 

 the environment of substances to which the gene responds adap- 

 tively. 



DAUERMODIFIKATIONEN AND DEPLETION MUTATIONS 



"Nongenic" Modifications 



Changes occur in cells which are relatively permanent on veg- 

 etative reproduction but are incapable of being transmitted through 

 the sexual cycle. These changes correspond to what we have 

 called depletion mutations and are apparently identical with the 

 changes which Jollos called Dauermodifikationen and correspond 

 to what Goldschmidt classified as the phenocopies. In other 

 words, a great variety of different kinds of changes may occur in 

 a cell which cannot be transmitted through the sexual cycle, but 

 which resemble gene mutations phenotypically. Another common 

 characteristic of the depletion mutation, the Dauermodifikation, 

 and the phenocopy is the frequency with which they can be induced, 

 in contrast to the relative rarity of the characteristic gene muta- 

 tion. The disadvantage of studying this phenomenon in Drosophila 

 is that the only means of propagation of a succeeding generation 

 in Drosophila is by the sexual mechanism and therefore the stabi- 

 lity of the variations in vegetative reproduction cannot be tested. 

 As a matter of fact, the view has become prevalent that modifica- 



