Clones; Transformation; Strand Recombination in Vitro 305 



QUESTIONS FOR DISCUSSION 



22.1. Which single characteristic of bacteria provides the greatest advantage for ge- 

 netic studies? Why? 



22.2. Assuming that all members of a clone are genetically identical, could sexual 

 processes have influenced the results of any of the experiments described in 

 this chapter? Explain. 



22.3. Distinguish between auxotrophic and prototrophic bacteria. 



22.4. Design an experiment to test whether the dye, acriflavin, is mutagenic in E. coli. 



22.5. Compare the "chromosome" of bacteria with that of man. 



22.6. Is the use of the phrase "bacterial chromosomal DNA" justified even though 

 bacteria do not contain typical chromosomes? Explain. 



22.7. What is meant by integration in genetics? Without using diagrams, describe 

 the mechanisms by which it may occur. 



22.8. List those features of crossing over which are difficult to explain on a copy- 

 choice basis. 



22.9. Discuss the genetic control of gene synthesis and gene degradation. 



22.10. Criticize the statement (p. 5) that genetic transmission can occur between gen- 

 erations only by means of a cellular bridge. 



22.11. On what basis is transformation classified as a type of genetic recombination 

 rather than as a mutation? Do you agree with this interpretation? Why? 



22.12. Devise an experiment to detect whether chain separation occurs during exten- 

 sive in vitro synthesis of DNA. 



22.13. Do the studies on transformation offer any clues as to the ploidy of Pneumococ- 

 cus? Explain. 



22.14. What kinds of problems would you investigate if you had a feasible method of 

 studying the fate of individual cells exposed to transforming DNA? 



22.15. What do studies of genetic transformation reveal regarding the genetic nature 

 of conserved and nonconserved chromosomal DNA? 



22.16. Redraw Figure 22-5 showing hypothetical base sequences in double-stranded 

 DNA. Has your drawing any bearing on your answer to question 22.8? 

 Explain. 



22.17. How can you explain the finding (p. 299) that the frequency of double trans- 

 formations for certain markers is sometimes somewhat less than the product of 

 the frequencies of the single transformations? 



22.18. Interspecific transformation in bacteria is rare or absent when the relative G + C 

 contents of host and donor differ. When the G + C contents are the same, 

 donor-host hybrid DNA's can form even when interspecific transformation is 

 rare. Discuss the relative values of G + C content, hybrid DNA formation, 

 and interspecific transformation in taxonomic studies of bacteria. 



