256 



CELL HEREDITY 



Control 



M 



a^bWcd 



tft* 



Euflavine 



FIGURE 9.7. Induction of 

 petite mutations by euflavin. 

 Pedigree analysis of single 

 yeast cells and tfieir descend- 

 ants grown in tfie presence 

 and absence of euflavin. The 

 first line of descendants repre- 

 sents the buds produced by 

 each treated cell, and the 

 second line represents one 

 bud from each of the first gen- 

 eration of buds. The pheno- 

 type of each cell was deter- 

 mined, by tests of the clone 

 developing from it, as the 

 presence or absence of cyto- 

 chrome oxidase. Black circles 

 represent wild type clones; 

 open circles represent petite 

 mutants (from Ephrussi and 

 Hottinguer, 1950, Nature, 

 166:956). 



cell extracts, particles with the morphological properties of mitochondria 

 are found in petite cells, but they are inactive in terminal oxidation. 

 The cytochrome spectrum of petite cells resembles that of normal yeast 

 grown anaerobically, and, consequently, one might expect that studies 

 of the shift from anaerobic to aerobic conditions in normal yeast could 

 shed some light on the nature of the petite mutation. Recently Slonimski 

 has reported evidence of a conversion of one of the enzymes in this 

 pathway — the flavoprotein, lactic dehydrogenase — from its anaerobic 

 form to its aerobic form when oxygen is supplied, rather than de novo 

 synthesis of the aerobic enzyme. 



Petite mutants resulting from a chromosomal gene mutation have been 

 called "segregational petites, in distinction to the "vegetative petites" 

 which result from alteration in a nonchromosomal gene. In crosses of 

 segregational x vegetative petites, the diploid zygote is normal in pheno- 

 type, and the progeny arising after meiosis segregate 2:2 for the chromo- 

 somal gene. These results are precisely the same as those observed in 

 crosses of segregational petites x normal strains. An important inference 

 from these results concerns the maintenance of the nonchromosomal de- 



