Section 2 — Recombination 



When different cultures, in which spontaneous 

 suppression of the mutant gene purple has taken 

 place, are crossed with wild type, the proportion 

 of unsuppressed purples appearing in the prog- 

 eny varies (between suppressors) from per 

 cent to about 19 per cent. The scatter of values is 

 continuous rather than discrete. Identification 

 of the expected reciprocal recombinant class 

 has been attempted, but unequivocal evidence 

 for its occurrence and for the 1 : 1 segregation of 

 suppressors has not been obtained. Evidence 

 from the resolution of dicaryons formed between 

 suppressed and unsuppressed cultures shows 

 however that suppression is not due to cyto- 

 plasmic factors. Suppressed cultures are quite 



stable and recombinant suppressed cultures, 

 from crosses with wild type, have exactly the 

 same characteristics as their parents with 

 respect to segregation of purples and comple- 

 mentation reactions. Infertility is frequent in 

 crosses involving suppressed purples. It is pos- 

 sible that the spontaneous suppression of purple 

 involves chromosomal changes, in which case 

 non-complementation between suppressors 

 which have different characteristic purple segre- 

 gations would be less surprising. 



1. D. Lewis, 1960; D. H. Morgan, 1961. 



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