THE LIMITS OF THE SUPER-GENE 



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Fig. 86. — Heterocaryosis in fungi. The heterocaryon contains nuclei of more than 

 one kind, with relative frequencies determined by external conditions. These nuclei 

 co-operate in action to produce a phenotype depending on the balance of all their 

 genes simultaneously. The conidia contain only one nucleus each, all in one row 

 having the same nucleus, and the relative frequencies of the rows with the different 

 nuclei affords a measure of the relative frequencies of the nuclei in the heterocaryon. 

 Three types of nuclei are illustrated, their ratio being 2 : i : i in both heterocaryon 

 and conidia. In Aspergillus the colour of the conidium is determined by its own 

 nucleus (as illustrated), but in PcniciUium it is determined by the genetic constitution 

 of the heterocaryon (based on Pontecorvo, 1946). 



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