FERTILE BREEDING STOCKS 



18-2 



^nd several viable ascospores were dissected from it. One of these 

 (CIA) produced a haplophase culture which fermented both galactose 

 and melibiose and copulated abundantly with our a haplophase No. 

 35 (g me) and produced a pedigree in which the a/a alleles segre- 

 gated regularly proving the a allele in S. carlsbergensis is identi- 

 cal to that in our breeding stock. However, the fermentative ability 

 of the cultures derived from the asci was segregated in 4:0 and 3:1 

 ratios in addition to the 2:2 ratios expected if a monohybrid mating 

 had been made. Our first interpretation of these data was that more 

 than a single pair of genes controlled the fermentation of both gal- 

 actose and melibiose. Since that time many additional data have 

 been accumulated from hybrids analyzed in the pedigree shown in 

 fig. 18-1; they will be considered in detail in the subsequent dis- 

 cussion. 



SACCHAROMYCtS 5ACCHAR0MYCES SACCHAROMTCES S^CHAROMTCES SKOiMOtftaS 

 MCROQ^KOKUS CEREVI^ TLD CfSSSm MRAK9 3 CARLJS^NSS CH^ 



lAG(WEAI^me X IB &(5TR0NG;n« 4G<ST]mjme 1156 CM M ^8i9 3^(M) 



L2J16| 

 RE&5KfiK>TONl 



R[&SBI?fMT)ONl 2^ 



MusT^ mm 0F+ X m&xk^pn 



ad MT^Z^ ' 



mONUE 



2152 



21S3 3)90)^^6 



215f 



ZJS y ^^ 260 X zh 





c^^^l 5d5XZ9 



X zloi 



m9xzm 



2660 X MJ51AfiDM/MT or 4 

 ADrrt 



RCGUARS[Gf?f:GAT10N 



2882 X 2791 X 2412 

 j 2998X2467 

 h309I X 3228 



35f3 X 4539 



49l25 4^ 4^409 



Fig. 18-1 Pedigree Showing how our Breeding Stocks have been 

 Developed. Four different "species" were crossbred to incorporate 

 their various differences in the stock. At seveSral stages in the 

 process irregular segregations occurred, especially when a heter- 

 ozygote was first made, later selection produced 2:2 segregations. 



S. microeUipsoideus is a non-fermenter of maltose, but most 

 of the haplophase cultures which were tested from No. 9 to No. 500 

 were capable of fermenting maltose. Occasional non-fermenters 

 were found and in some asci the ratio was 2:2. A backcross to the 

 original non-fermenter of galactose (lA g me) eventually pro- 

 duced No. 520 which was mated to No. 525, and in this pedigree 

 regular 2:2 segregations of mating type alleles and genes con- 



