22-9 THE YEAST CELL 



pantothenate than the cultures which had been originally classi- 

 fied as "synthesizers." 



Inoculum came from a slant of yeast extract agar. Cells were 

 suspended in 10 cc. of sterile distilled water and transfers to Burk- 

 holder's mediimi were made with a loop of this diluted suspension 

 to insure against transfer of vitamins. A small but uniform number 

 of cells was transferred in each loop. Irrespective of the concen- 

 tration of pantothenate in Burkholder's synthetic media none of these 

 original transfers failed to grow, but each grew after the delay in- 

 dicated on the graphs. Many other transfers were subsequently made 

 from one tube of Burkholder's sjmthetic medium to another with the 

 same concentration of pantothenate; all these resulted in growth. 



S. carlsbergensls (culture No. 2, fig. 22-1) completed growth in 

 all concentrations of pantothenate before 100 hours. The single hap- 

 loid offspring of S. carlsbergensls (No. 7, fig. CIA) is capable of 

 utilizing any available pantothenate as is shown by the beautifully 

 parallel curves on the different concentrations. A hybrid between 

 culture No. 7 and No. 5 produced the hybrid, culture No. 10, which 

 grew rapidly in deficient medium (fig. 22-1). When four haploid 

 progeny from hybrid No. 10, cultures No. 20, No. 21, No. 22 and No. 

 23 (fig. 22-3) were tested, all showed the ability to use whatever 

 pantothenate was available as evidenced by the parallel nature of the 

 curves for different concentrations. However, these four progeny 

 were all "synthesizers" of the vitamin; no clear-cut Mendelian segre- 

 gation occurred. This does not mean that the difference is not xmder 

 gene control, for this pedigree is one in which gene transformation 

 occurs frequently. 



ADAPTATION TO THE ABSENCE OF PANTOTHENATE 

 BY A REGULARLY SEGREGATING, SLOWLY 

 ADAPTING CULTURE 



Since the strains described in the preceding section did not segre- 

 gate in a regular Mendelian manner, the experiments were continued, 

 by Raut (1949) with pantothenate -dependent haploid strain 2154, from 

 a regularly segregating pedigree, in order to determine the genetic 

 nature of the adaptation. In addition to segregating regularly, strain 

 2154 also requires a longer time for adaptation to take place (over a 

 month). This strain was derived from the pedigree shown in Table 

 19-3. Critical selective breeding for several generations had pro- 

 duced regular segregations and considerably lengthened the time re- 

 quired for adaptation. Haploid clone 2154 came from an ascus con- 

 taining two dependent and two independent spores, as follows: 2151 -, 

 2152+, 2153 + and 2154 -, where "+" indicates ability to grow with- 

 out pantothenate added to the medium and "-" indicates inability to 

 grow under these conditions. In this pedigree whenever a pantothenate 



