22-27 



THE YEAST CELL 



Table 22-5 

 Rapidly-growing Mutants Detected in Culture III 



*The 4 large colonies picked up on the 76th and 79th days 

 showed only slight growth after 22 days when a few 

 hundred cells were inoculated into liquid test medium. 

 All of the colonies selected later showed appreciable 

 growth in 3 to 4 days after transfer to pantothenate- 

 free medium. 



dium, the time to visible growth is reduced to three to four weeks, 

 so this adaptation is transmitted vegetatively. The rate of growth 

 following the "primary" adaptation has been shown to be constant. 

 However, the rate is not the same in all cultures. The generation 

 time for culture HI at 30° C. is 82 hours, for culture I it is 40 hours 

 and for a third culture, not discussed further in this paper, it is 65 

 hours. The change occurs when there are relatively few cells pres- 

 ent. The secondary adaptation (apparently a gene mutation), result- 

 ing in cells which grow much more rapidly in the absence of panto- 

 thenate, occurs when a large number of cells is present. There is 

 variation in the rate of growth on pantothenate -free medium among 

 the rapidly -growing colonies which make it appear that there are 

 several levels of independence; both primary and secondary adapta- 

 tions may consist of several steps. 



