172 CHAPTER 20 



REFERENCES 



Cleland, R. E., "Some Aspects of Cyto-Genetics of Oenothera," Bot. Rev., 2:316-348, 1936. 



QUESTIONS FOR DISCUSSION 



20.1. What evidence can you present that the genes comprising the balanced lethal system 

 in Lamarckiana are different from those in biennis'} 



20.2. Discuss the statement: "All evening primroses in nature are constant hybrids." 



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

 of a ring? 



20.4. Can circles contain an odd number of chromosomes? Explain. 



20.5. What new investigations regarding the genetics and/or cytology of Oenothera does 

 the present Chapter suggest to you? 



20.6. List the principles of genetics you could have arrived at had Oenothera been the only 

 organism so far studied. 



20.7. If this Chapter contains no new principles of genetics, for what purpose do you 

 suppose it was written? 



20.8. Curly winged Drosophila mated together always produce some non-curly offspring. 

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

 But, when flies are mated that are both curly and plum only flies of this type occur 

 among the offspring. 



Defining your gene symbols, explain all three kinds of results. 



20.9. Draw a diagram representing 

 the appearance of a heterozy- 

 gous whole-arm translocation 

 in Drosophila at the time of 

 synapsis. Number the arms of 

 the chromosomes involved. 



What else would you require 

 in order that a mating of two 

 flies with this configuration pro- 

 duce only offspring of this type? 



20.10. Do you suppose that the pres- 

 ervation of heterozygosity has 

 an adaptive advantage in Oeno- 

 thera! In other organisms? 



Hugo De Vries (1 848- 1 935), pioneer 

 in the study of Oenothera genetics. 

 {By permission of Genetics, Inc., vol. 

 4, p. 1, 1919.) 



