372 CHAPTER 40 



in the last portion of this Chapter are highly speculation is identified as such, no perma- 

 speculative. (Speculation in science is per- nent scientific damage ensues.) In the 

 mitted, however, if it conforms to the facts Chapters that follow you should keep these 

 known at the time, and if it leads to expecta- ideas in mind, and search for more informa- 

 tions subject to test in feasible experiments. tion to test the correctness of part or all of 

 When these rules are followed, and the the hypotheses presented. 



SUMMARY AND CONCLUSIONS 



The free episome F may carry chromosomal markers, and chromosomes may carry only a 

 part of F. This results in a two-directional flow of genetic material between extrachromoso- 

 mal F and the chromosome, which represents a new type of genetic recombination. 



The chromosomal markers carried by free F are still capable of replication and of pheno- 

 typic function, having retained these genie characteristics though removed from the chro- 

 mosome. 



Colicines are the product of an episome. Episomes may exist in organisms more complex 

 than bacteria. The characteristics of centrosomes, kinetosomes, and centromeres suggest 

 that these show a present or past episomal relationship with each other. Elements like 

 Modulator and Dissociation have some of the properties of episomes. 



Speculation leads to the tentative concept that nucleotides may be shared by adjacent 

 cistrons. This might lead to suppressed or variegated phenotypic effects, chromosomal 

 breakage, and movement of cell organelles. The study of episomes and of episomal-like 

 factors may provide a test of the occurrence and consequences of nucleotide-sharing. 



REFERENCES 



Adelberg, E. A., and Burns, S. N., "Genetic Variation in the Sex Factor of Escherichia Coli," 

 J. Bact., 79:321-330, 1960; reprinted in Papers on Bacterial Genetics, Adelberg, E. A. 

 (Ed.), Boston, Little, Brown, 1960, pp. 353-362. 



Jacob, F., and Wollman, E. L., "Episomes, Added Genetic Elements" (in French), C. R. 

 Acad. Sci. (Paris), 247:154-156, 1958; translated and reprinted in Papers on Bacterial 

 Genetics, Adelberg, E. A. (Ed.), Boston, Little, Brown, 1960, pp. 398-400. 



Herskowitz, L H., "The Hypothesis of Nucleotide Sharing by Adjacent Functional Units 

 of DNA," (Abstr.) Genetics, 46:870, 1961. 



PoUister, A. W., and Pollister, P. F., "The Relation Between Centriole and Centromere in 

 Atypical Spermatogenesis of Viviparid Snails," Ann. N.Y. Acad. Sci., 45:1-48, 1943. 



Spencer, J. H., and ChargafF, E., "Pyrimidine Nucleotide Sequences in Deoxyribonucleic 

 Acids," Biochim. Biophys. Acta, 51:209-211, 1961. 



QUESTIONS FOR DISCUSSION 



40.1. Answer question 39.9 on page 365. 



40.2. Do all matings transfer F particles of one genotype or another? 



40.3. Discuss the relationship between the transmission of free F particles and of a segment 

 of the male chromosome. 



40.4. Discuss the reality of a bacterial "chromosome" and its linear arrangement. 



40.5. By what series of events can you explain the origin of strain P4x-1 from P4x? 



40.6. Specify a particular Hfr strain oi E. coli and tell how you would proceed to obtain 

 an F-Pro (proline) particle. 



