Induced Mutational Changes in Yeast 121 



spore formation there occurred segregation in respect of the 

 altered character. If we take into account the 4-spore asci, 

 all the spores of which germinated and produced separate 

 cultures, then all 16 asci obtained from these cultures showed 

 segregation in the ratio of 2 : 2, i.e. 2 spores of each ascus 

 formed sucrose-fermenting cultures and 2 formed sucrose- 

 nonfermenting cultures. It should be pointed out that, in all 

 cases, the difference in sugar-fermenting capacity of the 

 different cultures was very wxll pronounced: in fermenting 

 cultures fermentation began on the first or second day and 

 ended on the third or fourth day; in nonfermenting cultures 

 no sign of fermentation was observed for 30 days. 



The same results have been obtained in experiments with 

 cultures adapted to fermentation of maltose. In two cultures 

 obtained from cells adapted to fermentation of maltose, 11 

 asci were investigated : all of these showed segregation in the 

 ratio of 2 : 2, and here also the difference between fermenting 

 and non-fermenting cultures was clearly marked. 



Another type of heredity was detected in S. paradoxus 37, 

 adapted to fermentation of maltose. Out of 60 isolated spores 

 (nine 4-spore and eight 3-spore asci), 29 germinated and formed 

 cultures. All of these fermented maltose. However, among 

 the 4-spore asci not a single one was found in which all the 

 spores w^ould germinate and form cultures. Only 3 asci 

 formed 3 viable cultures each, and in 2 cases the third culture 

 died when reseeded into wort-agar. In one case, one viable 

 colony was formed in a culture among the mass of dead 

 cells. As regards the remaining asci, only 1 or 2 spores proved 

 to be viable. 



The fact that all 29 cultures obtained from single spores of 

 the altered cells formed maltose-fermenting cultures gives us 

 ground for suggesting that, in these cultures, segregation does 

 not occur in respect of the altered character. The most likely 

 assumption, in this case, would be that adaptation to fermenta- 

 tion of maltose occurs in the haploid phase of cell develop- 

 ment, i.e. in the time between germination of spores and 

 formation of the haploid cell, and fusion of this with a similar 



