18-5 



THE YEAST CELL 



inate after isolation, "died" means that the spore produced a small 

 haploid culture which could not be transferred. Haplophase No. 

 4911 was a fertile non-fermenter of sucrose and it was used to in- 

 troduce the character into our stocks in the series of steps shown 

 in fig. 18-3. Many irregular segregations occurred but eventually 



ISSS 



5x5 AxS 



3SSSS 2SSSS 



ISSSa 35SS4 



2SSa4 



A X S 



i6 , 3 SSa6 



9M*- 





AVS' 

 AXS 



3SSSa 

 ISSaa 



7=1 



Uaaa 



A xS 



ISaaa 



A X S 



35S>i 



ISS66 



A xS 



65S5- 

 ISSaa 

 75Sa' 



2555S' 



ISSSS AxS 

 SSSSa ISSSa 



AXS AxS 



ISSaa ZSSaa 

 ISaj- 



ZSSSa 

 155S5 



AX5 



1555S 



SMO 



Fig. 18-3 Irregular Segregations in the Sucrose Pedigree. 



a hybrid produced 2:2 segregations and the sucrose non-fermenting 

 allele was introduced into the complex stock. Some of our present 

 stocks contain 14 alleles, all of which segregate 2:2 in nearly every 

 ascus. 



HAPLOID NON-FERMENTERS FROM A WEAK FERMENTER 

 BY A STRONG FERMENTER HYBRID 



It is important to note that both the original nonfermenter of 

 galactose and the original nonfermenter of sucrose were derived 



