324 



GENETICS OF FUNGI 



o 



o 



o 

 o 



G 



Fig. 53. Diagrams to illustrate sex of ascospores of Neurospora tetraspervia, 

 conditioned bv whether sex is segregated at the first division of the primary 

 ascus nucleus or at the second nuclear division. Above. Segregation at the 

 first division, C, resulting in four free nuclei of one sex after the third 

 division, and four nuclei of the other sex, E. Two of the four spores 

 formed are therefore of one sex, F, and two of the other. The two upper 

 ascospores may both be + (G) with the lower pair, or the pairs may occupy 

 the reverse positions. Below. Sex not separated in C at the first division 

 of the fusion nucleus, but separated in the second division. When asco- 

 spores are delimited, each contains part + and — , F, or else sex may not 

 segregate at all, and each nucleus is as shown in G. (Adapted from Dodge.) 



