CYTOPLASMIC INHERITANCE 27-16 



tions are extraordinarily unstable changes because they are never 

 transmitted to the next sexual generation; they are considered to 

 be simply temporary changes and therefore to be imposed upon the 

 cytoplasm rather than controlled by genes. It is probable, however, 

 from the great stability of similar variations in the vegetative 

 phase in yeast cells that the so-called modifications in Drosophila 

 may be highly stable, like the Dauermodifikationen of JoUos in 

 Paramecium, and that they may be capable of persisting indefinite- 

 ly throughout the vegetative phases of the cell -cycle, but disap- 

 pear on sexual reproduction in the flies just as the Dauermodifi- 

 kationen of Paramecia disappear on sexual reproduction. Droso- 

 phila workers have formed the opinion (probably incorrectly) that 

 modifications are impermanent because Drosophila only reproduce 

 sexually and each new generation is obtained by a sexual fusion, - 

 a process which invariably causes the modification to disappear. 



Jollos (1913) originally defined Dauermodifikationen as persis- 

 tent transmissible changes in a cell which disappear slowly on 

 vegetative reproduction and immediately on sexual reproduction. 

 He insisted on recognition of the distinction between (1) persistent 

 segregating gene mutations. (2) somatic modifications which disap- 

 pear when the environment changes, and (3) persistent modifica- 

 tions (Dauermodifikationen) which are induced by a change in the 

 environment which are relatively stable on vegetative reproduc- 

 tion but which disappear immediately when outcrossed. 



This definition of Dauermodifikationen coincides with what we 

 have called a depletion mutation. Jollos' observations were so 

 difficult to reconcile with classical gene theory that many Ameri- 

 can geneticists, including myself (1935), interpreted them as indi- 

 cating that he had been dealing with standard gene mutations which 

 were selected in an adverse environment and eliminated by re- 

 duction of the heterozygous diploid nucleus. 



However, our observations of depletion mutations and the 

 critical tetrad analysis of the heterozygotes support the validity 

 of Jollos' original observations on Paramecium. Our observa- 

 tions support Jollos', but our interpretation is different. I 

 have designated variations of this type "depletion mutations" to 

 suggest that the effect is genie rather than cytoplasmic as pro- 

 posed by Jollos. 



Cytogenes 



In our earlier papers on non-Mendelian and so-called cyto- 

 plasmic inheritance, I coined the word "cytogene" to designate a 

 hypothetical autonomous cjrtoplasmic entity produced by the 

 chromosome. Subsequent experiments failed to support the view 

 that an autonomous cytoplasmic entity was present in the cell. 

 I attempted to change the definition of the word to conform to these 



