NONCHROMOSOMAL GENES 



239 



nucleus and probably no cytoplasm. Thus, reciprocal crosses can be 

 made with this material. 



As shown in Figure 9.2, the poky trait is transmitted to all progeny 

 when carried by the maternal parent, and to none when carried by the 

 conidial parent. The difference in reciprocal crosses may result from 

 the fact that conidia transmit little or no cytoplasm, but there is no 

 direct evidence on this point. 



The poky mutant and a similar strain subsequently isolated (mi-3) 

 have been further investigated with respect to their stability and to the 

 biochemical basis of the poky phenotype. There has been no change in 



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No poky progeny All poky progeny 



oand« = chromosomal gene differences 



FIGURE 9.2. Nonchromosomal inheritance in Neurospora. From the mycelium of o 

 poky strain, both female (protoperithecio) and male (conidia) gametes are formed, so 

 that reciprocal crosses can be performed with a wild-type strain. When poky is used 

 as female parent, all the progeny are poky, and in the reciprocal cross all the progeny 

 are nonpoky; in both cases, segregation is 1 : 1 for other chromosomal genes segregating 

 in the cross (after Mitchell and Mitchell, 1952, Proc. Natl. Acad. Sci. Wash., 38:442). 



