CARL C. LINDEGREN 



Southern Illinois Universify 



Chapter 16 



Genetics and Cytology 

 of Soccharomyces 



In the middle of the last century, Buchner ground up yeast cells and proved 

 that the cell-free filtrate contained a substance capable of fermenting sugar. 

 This experiment settled a heated controversy between Liebig and Pasteur 

 concerning whether or not living structures were essential to fermentation. 

 The substance responsible for the fermentation was called an enzyme, the 

 word being derived from the Greek and meaning "in yeast." Since that time, 

 yeast has been the organism of choice for experimenting in enzyme chemistry 

 because of the abundant supply obtainable from breweries and from factories 

 producing bakers' yeast. The biochemistr}^ of fermentation has provided the 

 foundation for our present understanding of the biochemistry of respiration 

 and of muscular contraction — two of the fundamental problems which have 

 intrigued biologists. It has led to an understanding of vitamins and through 

 them to an understanding of chemotherapy. 



BIOCHEMICAL DEFECTS AS GENE MARKERS 

 The work of Beadle and Tatum has popularized the generally accepted 

 view that enzymes are derived somehow or other from genes. Their work 

 initiated a new interest in biochemical genetics. They showed that the in- 

 activation of a specific gene caused a deficiency which could be met by sup- 

 plying a specific chemical. Vitamins, amino acids, purines, and pyrimidines 

 were the substances chosen in this analysis. They used the fungus, Neuro- 

 spora, because its life cycle had been thoroughly worked out by B. O. Dodge 

 and because the Lindegrens had shown by genetical analysis that it contained 

 conventional chromosomes on which genes, arranged in linear order, could 

 be mapped by the standard procedures used in studying corn and the fruit 



fly- 



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