266 



CELL HEREDITY 



sex ratios in Dwsophila, sex detcrmiiiatioii in bacteria, and toxin produc- 

 tion by the diphtheria bacterium. 



Both the F factor and lysogenic phage, discussed in Chapter 5, are 

 examples of infectious agents which can exhibit a high degree of inte- 



Killer Sensitive 



Killer Sensitive 



Parents 



•: I 



|: I 



Conjugants 



Fi progeny 



Killer Sensitive 



Without 



cytoplasmic 



exchange 



Killer 



Killer 



With 



cytoplasmic 



exchange 



FIGURE 9.12. Cytoplasmic inheritance of the killer trait. Killer cells are shaded, 

 sensitive cells clear. In the usual conjugation, there is exchange of nuclei but little 

 or no cytoplasmic exchange. The phenotype of the F j progeny with respect to the 

 killer trait is determined by the parent which contributed the cytoplasm. However, if 

 extensive cytoplasmic exchange is allowed to occur, then all the Fj progeny inherit the 

 killer trait (after Beale, 1954, The Genetics of Paramecium Aurelia, Cambridge, The 

 University Press). 



