240 CHAPTER 17 



QUESTIONS FOR DISCUSSION 



17.1. Whal evidence can you present for saying that the genes which make up the 

 balanced lethal system in Lamarckiana arc different from those in biennisl 



17.2. Discuss the following statement: "All evening primroses found in nature are 

 constant hyhrids." 



17.3. With respect to chromosomes, how does the origin of a circle differ from the 

 origin of a ring? 



17.4. Can a circle contain an odd number o\ chromosomes? Explain. 



17.5. What new investigations regarding the genetics and or cytology of Oenothera 

 has this chapter suggested to you? 



17.6. List the genetic principles you could have deduced had Oenothera been the only 

 organism studied so far. 



17.7. If this chapter contains no new principles of genetics, why do you suppose it 

 was written? 



17.8. Curly-winged Drosophila mated together always produce some non-curly off- 

 spring. Plum eye-colored flies mated together always produce some non-plum 

 offspring. But, when flies that are both curly and plum are mated together, only 

 flies of this type occur among the offspring. Explain all three kinds of results 

 and define your symbols. 



17.9. (a) Draw a diagram representing a heterozygous whole-arm translocation in 

 Drosophila at the time of synapsis. Number all chromosome arms involved, 

 (b) What would be required for a mating between two flies with this constitu- 

 tion to produce offspring flies only of this type? 



17.10. Do you suppose that the preservation of heterozygosity has an adaptive ad- 

 vantage in Oenothera? In other organisms? 



17.1 1. Discuss the evolutionary flexibility of the genus Oenothera and Drosophila. 



17.12. Is the balanced lethal system in Oenothera part of its genetic load? Explain. 

 If so, are the lethals components of a balanced load or a mutational load? 

 Explain. 



17.13. Compare the genetic effects of ionizing radiation on populations of Oenothera 

 and Drosophila. 



17.14. Explain how a Drosophila zygote formed with a sperm carrying a centric, 

 grossly-deleted Y chromosome can develop into a fertile male. 



