GENE CONVERSION 



26-30 



The original gg stock used as a parent in the genetical analysis 

 appeared as a mutant in a pedigree in which regular segregation 

 for the G/g alleles had been clearly established and in which less 

 than one percent of the individual cultures were gg. Long-term 

 adapting (gg) offspring of the original mutant (grown on glucose) 

 were mated with standard G cultures and produced extensive pedi- 

 grees in which the three phenotypes, G, g, and gg, were distinguish- 

 ed. In heterozygous matings half of the progeny were G while gg 

 and g clones were divided unequally among the remaining individ- 

 uals; nearly 35 percent of the offspring were gg (Table 26-15). 



Table 26-15 



Distribution of $2 asci obtained froM G by g^ hybrids. 

 Each ascus was proved to be a hybrid by use of frov. J to 

 S other genetical markers. The parents used for each 

 mating are indicated by the serial numbers heading the 

 columns. The number of asci of each type is indicated in 

 each column and the total in the final column. Only asci 

 producing four viable spores are included. It is signif- 

 icant that most of the non-fermenters arose from the mat- 

 ing of 6145 X 3403, 



However, when sibling g clones derived from this pedigree were 

 mated to G at least 25 percent of the progeny were gg (Table 

 26-16), suggesting that the g phenotype may be indistinguishable 

 from gg in the same pedigree. Table 3 shows the types of tetrads 

 derived from mating of G by g in which the g cultures were all 

 descendents of gg parents. The considerable number of gg cul- 

 tures appearing among the offsprir^ indicates that both G and g 

 individuals descended from go parents transmit the capacity for a 

 high mutation rate of g to G. it should be emphasized that in the 

 extensive analyses of CVg hybrids previously made in this labora- 

 tory, only an extremely small fraction of the progeny were slow 



