284 M. Westergaard 



the cytoplasm (usually by maternal inheritance) whereas the 

 latter is not inherited at all. There are numerous examples of 

 cytoplasmic inheritance in higher organisms, the best probably 

 being concerned with the inheritance of chloroplast defects in 

 higher plants. In micro-organisms the vegetative "petite" 

 mutant in yeast, which lacks certain enzymes in the cyto- 

 chrome system, may be quoted as an example (see Ephrussi, 

 1953). The "poky" mutant of Neurospora is another (Mitchell, 

 Mitchell and Tissieres, 1953), and the genetical studies of 

 Paramecium have revealed many interesting examples of 

 cytoplasmic inheritance (see Beale, 1954). 



The work of Gale, Spiegelman and others (cf. Gale and 

 Folkes, 1954; Spiegelman, Halvorson and Ben-Ishai, 1955), 

 in which enzyme synthesis is blocked by inhibition of RNA 

 synthesis, would of course be another good example of a 

 phenotypic event (lack of enzyme synthesis) which is due to 

 blockage of the decoding system. 



To complete the model we shall identify changes in the 

 information system with mutations, including intragenic 

 point-mutations as well as intergenic mutations resulting 

 from one or two breaks in the chromosome thread, and even 

 changes due to aneuploidy and polyploidy. 



In brief, in our information-translation-receptor frame- 

 work we may identify (1) "receptor events": modifications 

 and phenocopies in higher organisms; specific enzyme induc- 

 tion, clonal variation, and "physiological adaptation" in 

 bacteria; (2) "translation events " : cytoplasmic changes (muta- 

 tions), especially those which affect the mitochondria or 

 plastids; (3) "information events" which would be nuclear 

 mutations. 



In sexual organisms, the Mendelian crossing experiment 

 would decide which type of event has occurred, because 

 receptor events are not transmitted to sexual offspring, 

 translation events show non-Mendelian, mostly maternal 

 inheritance, whereas information events show Mendelian 

 inheritance. 



What are the possibilities for a similar discrimination 



