27-17 THE YEAST CELL 



new concepts. However, since the word was originally defined to 

 describe an autonomous entity, this was an improper thing to do. 

 It seems best now to discard the word, and this move is even more 

 strongly indicated since several who are conversant with the situa- 

 tion seem to have confused "cytogene" with "plasmagene." 



Haplophase Variability and Diplophase Stability 

 in terms of the Plasmagene Hypothesis 



Since the depletion mutation cannot pass through the zygote, 

 one might argue correctly, on a formal basis, that it involves a 

 change in the cytoplasm. However, haplophase cultures produce 

 an abundance of different kinds of stable variants, while diplophase 

 cultures are almost completely free from variability. If the vari- 

 ability of the haplophase were due to competition between plasma - 

 genes, a corresponding variability would be expected in the diplo- 

 phase. The regular uniformity of the diplophase (which contrasts 

 sharply with the "mutability" of the haplophase) supports the view 

 that plasmagenes do not exist. There is no reason why plasma- 

 genes could not be lost as readily in the diplophase as in the haplo- 

 phase; therefore, the contrast in variability in the two conditions 

 is a strong argument against the plasmagene hypothesis. The 

 uniformity in the diplophase may be due to the insurance provided 

 by the paired condition; if a gene suffers a temporary loss of a 

 gene -component, it is immediately repaired by its allele. 



