22-39 THE YEAST CELL 



accounted for by slow synthesis of pantothenate by the recessive 

 presumably non-synthesizing alleles. As cell population increases, 

 probability of a gene mutation occurring increases. When such a 

 mutation occurs, there is a sharp increase in rate of growth, - the 

 "secondary" adaptation. The decrease in time required for the 

 secondary adaptation to occur on the addition of minute amounts of 

 pantothenate is due to a slightly increased rate of growth and hence 

 a greater number of cells and a greater probability of mutation. 

 The time required for the primary adaptation to the medium to take 

 place appears to be shortened by the addition of small amounts of 

 pantothenate. 



