30 CHAPTER 2 



QUESTIONS FOR DISCUSSION 



2.1. Can sexuall) reproducing organisms reproduce asexually? Is the reverse true? 

 Explain. 



2.2. What arc the similarities and differences between mitosis and meiosis? 



2.3. Suppose the meiotic process had never evolved. What do you think would have 

 been the consequence? 



2.4. Certain unusual chromosomes are rings rather than rods. Could a ring chromo- 

 some, during meiosis. have any difficulty that a rod chromosome would not have? 

 Explain. 



2.5. How main hivalents are present at metaphase I in man? Corn? The garden pea? 



2.6. Discuss the statement: During meiosis. each segment of a chromosome segregates 

 independently of its homologous segment and of all other chromosome segments. 



2.7. Argue against the hypothesis that the physical hasis of genetic material lies in 

 the chromosomes. 



2.8. What do you suppose happens during meiosis in individuals possessing an odd 

 numher of chromosomes? 



2.9. Suppose an animal has a diploid chromosome number ol six. What proportion 

 of all its gametes would receive replicas of all the centromeres originally derived 

 from the father? From the mother? From either the father or mother? From 

 both the father and mother? 



2.10. What do you suppose is meant by the expression "first division segregation"? 

 "Second division segregation"? If exchanges giving rise to chiasmata can occur 

 at a variety of positions along the chromosome, under what circumstances can a 

 given chromosomal segment undergo first division segregation? Second division 

 segregation? 



2.11. If you saw a single cell at metaphase. how could you tell whether the cell was 

 undergoing mitosis, metaphase I, or metaphase 11 at the time it was fixed and 

 stained? 



2.12. What advantages do the following organisms offer lor the study of cytology 

 and/or of the genetic material: Drosophila? Corn? Neurospora? 



2.13. What are the major differences between spermatogenesis and oogenesis in 

 Drosophila? 



2.14. Suppose a pair of originally identical homologous chromosomes having arms of 

 equal length was changed permanently so that one gained a large knob at one end 

 and the other a small knob at the opposite end. Draw the appearance of these 

 new homologs (a) at mitotic prophase and (b) at diplonema. Draw the appear- 

 ance of all the monads in part b as seen at telophase II. 



2.15. Is the female sex cell of man or Drosophila ever haploid? Explain. 



2.16. How does a monad at diplonema differ from the same monad at telophase II? 



2.17. Can you suggest any functions which the polar nuclei in Drosophila oogenesis 

 may serve? 



2.18. Is mitosis in triploid endosperm expected to be normal? Why? 



