Questions and Problems 183 



stipules (s) to normal, and green pod (v) to purple (V). In the backcross 



Xbsv, the following phenotypes were obtained: 166 B S V : 



b s V 



14 B S V : 3 B s V : 70 b S V : 76 B s V : 2 b S V : 14 b s V : 146 b s V. 



Plot these genes on their chromosomes. 



5. Determine the percentage of double crossing over and determine 

 coincidence in problem 4. 



6. Using the chromosome map you obtained in problem 4, calculate 

 the expected ratio for families of 400 plants if the crosses were B sv / 

 bSVXhsv/bsv or BsV/bSvXhsv/bsv. 



7. What would be the expected ratios of the offspring of the following 

 crosses: BSV/bsvXbsv/bsv; Bsv/bSvXbsv/bsv; BsV/ 

 b s V X b s V / b s v] b S V / b s V X b s v / b s v? 



8. A three-point test in maize involving the genes 02, gl, and ij give 

 the following counts (data from Singleton in Genetics) : 



Plot these genes on their chromosomes and determine coincidence. 



9. In Drosophila melanogaster, the genes ct (cut wing) and v (vermilion 

 eye) are on the X chromosome and are 13 map units apart. If a ++ / d y 

 female were mated with a double recessive male, what would be the 

 expected ratio in both sexes of the offspring? Would there be any double 

 crossings over involving ct, v, and sex? 



10. The gene s (sable body) in Drosophila melanogaster is on the X chro- 

 mosome 10 map units from v. What would be the expected ratio in the 

 offspring from the cross + s / v + X v s? 



11. Using the information in problems 9 and 10, what would be the 

 expected ratios of offspring from the cross +++ / ctv s X ctv si The 

 order of the genes is ct-v-s. What would be the expected percentage 

 of double crossovers? 



12. In Drosophila melanogaster, gene b (black body) is on the second 

 chromosome and is approximately 27 units to the left of gene c (curved 

 wing) ; gene sp (speck) is approximately 32 units to the right of c. What 

 offspring should be expected from the cross +++ / bcsp Xbc sp/b c sp? 



13. Considering the same genes as m problem 12, what offspring should 

 be expected from the cross b c sp / b c sp X +++ /be sp? 



14. In Pisum, thick pod wall (n) is recessive to thin (N), keeled wings 

 (k) are recessive to normal (K) , and normal seed (q) is recessive to aborted 



