196 CHAPTER 22 



Lewis, E. B., "The Pseudoallelism of White and Apricot in Drosophila Melanogaster," 

 Proc. Nat. Acad. Sci., U.S., 38:953 961, 1952. 



Muller, H. J., Prokofyeva-Belgovskaya, A. A., and Kossikov, K. V., "Unequal Crossingover 

 in the Bar Mutant as a Result of Duplication of a Minute Chromosome Section," 

 C. R. (Dokl.) Acad. Sci., U.R.S.S., N.S., l(10):87-88, 1936. 



Sturtevant, A. H., "The Effects of Unequal Crossingover at the Bar Locus in Drosophila," 

 Genetics, 10:117-147, 1925. Reprinted in Classic Papers in Genetics, Peters, J. A. 

 (Ed.), Englewood Cliffs, N.J., Prentice-Hall, 1959, pp. 124-148. 



QUESTIONS FOR DISCUSSION 



22.1. If a novel phenotypic change is associated with a qualitative or quantitative change 

 in the genetic material, how can you decide whether to attribute the effect to mutation 

 or to position effect? 



22.2. Do you expect that position effects will be found in most sexually reproducing or- 

 ganisms? Why? 



22.3. Is there any evidence that crossing over is ever unequal? Explain. 



22.4. Should pseudoalleles be considered to be subgenes (parts of one gene) rather than 

 separate, nonallelic genes? Explain. 



22.5. Does position effect require pseudoallelism for its detection? Explain. Is the reverse 

 true? Explain. 



22.6. What is the minimum number needed, of genotypic alternatives for a "locus," in order 

 to test whether it shows a cis-trans position effect? Explain. 



Can one of the alternatives be a deficiency for all or part of the region under investi- 

 gation? Why? 



22.7. Can position effect occur in haploids? Why? 



22.8. How would you proceed to test whether two recessive mutants in Drosophila that are 

 apparently alleles of the X-linked gene, v+ (normal allele of vermilion eye color), are 

 pseudoalleles? 



