200 



CELL HEREDITY 



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FIGURE 7.9 (a). Segregation of a gene pair controlling light and dark spore wall color 

 in ordered asci of the fungus Sordaria. Only 4:4 segregations are seen in this group. 

 The gene-centromere map distance can be computed directly from the frequency of asci 

 showing other than 4 light: 4 dark spores in linear array. 



(fa). An aberrant ascus from the same cross as in a, with 6:2 segregation. 



(c). An aberrant ascus from the same cross with 5:3 segregation (from L. S. Olive, 

 unpublished). 



