GENETIC CONTROL OF CELL INTEGRATION 



349 



The relation between genetic determination of antigenicity and cyto- 

 plasmic determination of expression is shown graphically in Figure 11.20. 

 Mating was carried out between animals of one stock grown at 25° C 

 and therefore expressing their G antigen, and the other stock, grown at 

 29° C, expressing the D antigen. After conjugation, all F, animals whose 

 cytoplasm came from a G parent, contained a mixture of 60G and 90G; 



Parents 



Fj animals 

 after 5 fissions 



Fi animals 

 finally at 25°C 



90G + 60G 



90G + 60G 



90 D + 60 D 



90D + 60D 



90G + 60G 



90 D + 60 D 



Fj animals 

 finally at 29°C 



G & D refer to expressed antigens. 



d, g, s refer to gene loci, with unexpressed genes in parentheses. 



FIGURE 1 1 .20. Inheritance of antigenicity in Paramecium. In a cross between 

 animals of strain 90 grown at 25° C (and therefore expressing their g gene, 90G) 

 and animals of strain 60 grown at 29° C (expressing their d gene, 60D) the Fj 

 progeny express antigens from both parents, and are therefore 60 + 90. Initially, the 

 progeny inheriting cytoplasm from the G parent, are 60G + 90G while those from the 

 D parent are 60D + 90D. Subsequently, all Fj animals revert to the state deter- 

 mined by the temperature at which they are being kept (from Beale, 1954, The 

 Genetics of Paramecium Aurelia, Cambridge, The University Press). 



