Genes — Nature and Consequence 451 



ent, and future uses and importance of game, which I trust you have found stimu- 



genetics is given in Supplement V. Some of lating. But I also hope the adventure is not 



the questions posed at the ends of various completed for you, as it surely is not for me. 



Chapters also indicate various uses to which Let us look to a future in which we continue 



genetics has been or may be put. rapidly to increase our knowledge about the 



We have come to the epd of our thinking nature and consequence of genes, 



REFERENCES 



Allen, J. M. (Ed.), The Molecular Control of Cellular Activity, New York, McGraw-Hill, 

 1961. 



Cellular Regulatory Mechanisms, Cold Spr. Harb. Symp. Quant. Biol., 26, 1962. 



Champe, S. P., and Benzer, S., "Reversal of Mutant Phenotypes by 5-Fluorouracil: An 

 Approach to Nucleotide Sequences in Messenger-RNA," Proc. Nat. Acad. Sci., 

 U.S., 48:532-546, 1962. 



Fresco, J. R., and Straus, D. B., "Biosynthetic Polynucleotides: Models of Biological 

 Templates," Amer. Sci., 50:158-179, 1962. 



Mitchell, J. S. (Ed.), The Cell Nucleus, New York, Academic Press, 1960. 



Muller, H. J., "Genetic Nucleic Acid: Key Material in the Origin of Life," Perspectives in 

 Biol, and Med., 5 (No. 1, Autumn) :l-23, 1961. 



Niu, M. C, Cordova, C. C, and Niu, L. C, "Ribonucleic Acid-Induced Changes in Mam- 

 malian Cells," Proc. Nat. Acad. Sci., U.S., 47:1689-1700, 1961. 



Sager, R., and Ryan, F. J., Cell Heredity, New York, Wiley, 1961. 



Strauss, B. S., An Outline of Chemical Genetics, Philadelphia, Saunders, 1960. 



QUESTIONS FOR DISCUSSION 



49.1. Of what value are operational definitions of a gene? 



49.2. What is your present definition of a gene? 



49.3. In what respects has the concept of the gene been static and in what respects has it 

 been dynamic, in the course of this book? 



49.4. Define the recon and the cistron in chemical terms. 



49.5. Ignoring its chemical composition, what are the other characteristics of a cistron? 

 A recon? 



49.6. How would you now define a mutant? 



49.7. Is the recon a single nucleotide or a single nucleotide pair? Explain. 



49.8. Discuss two areas of future investigation which you believe might provide basic 

 information relative to the nature of the gene. 



49.9. If a "replicon" is defined as the smallest unit of the genetic material capable of replica- 

 tion, discuss what is already known about it. What questions can you ask about it; 

 whose answers are yet unknown? 



49.10. The work of R. W. Briggs and T. J. King on nuclear transplantation proves that 

 development involves irreversible changes in the nucleus. Should such changes be 

 described as mutations? Explain. 



49.11. Compare the terminal nucleosides of TMV and transfer RNA. What can you imply 

 from this comparison? 



49.12. What do you consider to be the essential characteristics of genetic material? 



