380 



CHAP I IK 29 



Tracy M. Sonnhborn. about I960. 



SUMMARY AND CONCLUSIONS 



Nucleated cells may contain an extensive system of extranuclear genes. In some cases 

 the extranuclear genes seem to be foreign organisms (viruses, kappa, and probably 

 sigma ) ; in other cases they appear to be associated with normal constituents of the 

 cell (plastids, mitochondria, centrosomes, kinetosomes, and kinetoplasts). The char- 

 acteristics of centrosomes, kinetosomes, and centromeres suggest a past or present epi- 

 somal interrelationship. The DNA in plastids and mitochondria has yet to be directly 

 connected with the activity of specific genes. 



Nuclear and extranuclear genes are already known to be interrelated in two ways: 

 the former can mutate the latter, and both may interact in the production of a par- 

 ticular phenotype. 



REFERENCES 



Barigozzi, C, "Relationship Between Cytoplasm and Chromosome in the Transmission 

 of Melanotic Tumours in Drosophila," in Biological Organization, pp. 73-89, 

 New York: Academic Press, 1963. 



Beale, G. H., The Genetics of Paramecium Amelia, Cambridge: Cambridge Univer- 

 sity Press, 1954. 



Campbell, A., "Conditions for the Existence of Bacteriophage," Evolution, 15:153- 

 165, 1961. 



Chevremont, M., "Cytoplasmic Deoxyribonucleic Acids: Their Mitochondrial Locali- 

 zation and Synthesis in Somatic Cells Under Experimental Conditions and Dur- 

 ing the Normal Cell Cycle in Relation to the Preparation for Mitosis," Sympos. 

 Int. Soc. for Cell Biol., 2:323-331, 1963. 



