



^Smr^tkii 







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7 





Fig. 13-1 The four haplgphase cultures derived from the four 

 spores of a single ascus of Saccharomyces cerevisiae (A» B, C and 

 D) and the results of pairing these cultures in all possible com- 

 binations. A X D and B x C pairings do not result in copulations. 

 The A X B pairing results in copulation, and the zygotes are much 

 larger than the cells found in either A or B alone, suggesting 

 that the hybrid is more vigorous than either parent. The same 

 increase in size is observed in the C x D, A x C, and B x D pairing 



13-2 



