188 PROTOZOOLOGY 



clones: one is a killer and the other is sensitive. He was able to dem- 

 onstrate that the Fi killer clones are those that derive their cyto- 

 plasm from the killer parent and the Fi sensitive clones are those 

 which contain the cytoplasm of the sensitive parent — a result con- 

 tradictory to the hitherto prevailing notion that the two exconju- 

 gants possess the same genotype and should produce clones alike 

 in their hereditary characters. Through a series of experiments, he 

 has come to realize that there exist certain "relations between a 

 gene and a cytoplasmic substance, both of which are required for 

 the development of a hereditary character. When some of the cyto- 

 plasmic substance is present, the gene controls its continued produc- 

 tion; but when the cytoplasmic substance is absent, the gene cannot 

 initiate its production. Addition of the cytoplasmic substance to an 

 organism, lacking the character dependent on it, but containing the 

 required gene, results in the continued production of the substance, 

 in the development of the character determined by the combined 

 presence of gene and cytoplasmic substance, and in the hereditary 

 maintenance of the character in successive generations." 



References 



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