GENETICAL CHARAaERS 11-14 



This introduction will serve to point out the many complications 

 which have arisen in the genetlcal analysis of fermentative ability 

 of yeasts. Our analyses have concentrated on the discovery of sin- 

 gle gene differences and we have been successful in developing 

 stocks differentiated by single gene differences with regard to galac- 

 tose, melibiose, maltose, alpha methyl glucoside and sucrose. These 

 stocks are referred to as "fermenters" and "nonfermenters" with 

 the reservations noted above. 



GALACTOSE - MELIBIOSE FERMENTATION 



Over 1,000 asci have been analyzed in which these two alleles 

 segregate independently of each other; the gene controlling ability 

 to ferment galactose does not interact with the gene controlling 

 the ability to hydrolyze melibiose. The existence of a yeast capa- 

 ble of fermenting melibiose, but incapable of fermenting galactose 

 raised an interesting point since melibiose is a disaccharide con- 

 taining dextrose and galactose. Fermentation tubes were inoculated 

 with the four different genotypes and after ten days, each tube was 

 tested for the presence of residual galactose by the mucic acid test. 

 The following table shows the results: 



TESTS FOR THE PRESENCE OF GALACTOSE IN 

 FERMENTATION TUBES AFTER TEN DAYS 



Residual melibiose is hydrolyzed by the nitric acid and also 

 produces mucic acid. These results suggest that the ME gene con- 

 trols the production of a hydrolytic enzyme which breaks melibi- 

 ose down to dextrose and galactose. In the absence of the gene, the 

 dextrose is fermented and the galactose is left behind. 



RAFFINOSE 



Raffinose is a trisaccharide in which fructose, dextrose, and 

 galactose are linked together, with dextrose as the central molecule. 

 The fructose and dextrose molecules in raffinose are united by a 

 sucrose linkage and the ability to ferment one -third raffinose de- 

 pends on the presence of the sucrose gene, which controls the pro- 

 duction of a hydrolytic enzyme that hydrolyzes raffinose into fruc- 

 tose and melibiose. The fructose molecule is fermented and the re- 

 sidual melibiose is left behind. 



