184 Locating Genes on Chromosomes 



cotyledon (Q). A cross NN KK qq X tin kk QQ gave the following 

 phenotypes: 



7 . 5 per cent thin pod, normal wings, aborted cotyledon 



17 . 5 per cent thin pod, normal wings, normal seed 



7.5 per cent thin pod, keeled wings, aborted cotyledon 



17 . 5 per cent thick pod, normal wings, aborted cotyledon 



17.5 per cent thin pod, keeled wings, normal seed 



7.5 per cent thick pod, normal wings, normal seed 



17.5 per cent thick pod, keeled wings, aborted cotyledon 



7 . 5 per cent thick pod, keeled wings, normal seed 



Plot these genes on their chromosomes or chromosome. 



15. What would be the approximate ratio of the types in problem 14 

 if the cross was NN KK QQ X nn kk qq'l 



16. What would be the approximate ratio of the types in problem 14 

 if the cross was Nn Kk Qq X Nn Kk Qq? 



17. In maize, zb produces zebra striping, Tu produces tunicate ear, 

 and gl produces glossy seedling. The following results were obtained 

 from individual sellings (data from Hayes and Chang in Genetics) : 



Zb Tu /zbtuX Zb Tu / zb tu gave 410 Zb Tu : 64 Zb tu : 64 zb Tu : 

 90 zb tu. 



Zb gl / zbGlX Zb gl / zb Gl gave 326 Zb Gl : 148 Zb gl : 135 zb Gl : 19 

 zb gl. 



Tu gl /tuGlX Tu gl / tu Gl gave 314 Tu Gl : 160 Tu gl : 147 tu Gl : 

 7 tu gl. 



Is there any evidence of linkage? If so, determine the percentage and 

 plot the genes on their chromosome. 



18. Suppose you have the following three different strains of the same 

 species of plant: aa BB cc, aabbCC, and AaBbCc. You desire to 

 determine whether these genes are linked. Outline the complete pro- 

 cedure you would use to determine whether there was any linkage. 



19. In using a three-point test, must all the linkages involved be in 

 either the coupling or the repulsion phase? 



20. In Nemesia strumosa, orange (0) is dominant to white (o); a 

 strain of oo plants was found which had a recessive gene for blue-margin 

 (bm). When a white, blue-margin plant was crossed with an orange, the 

 offspring were 18 orange : 19 blue-margin. Is there any evidence of 

 linkage? Is it conclusive? 



21. If genes a and b are on the same chromosome but show 50 per cent 

 crossing over, does this indicate that no chiasmata are formed between 

 a and 6? 



22. Crossing over between the following genes was observed: a and b, 

 30 per cent; a and c, 50 per cent; b and c, 20 per cent; c and d, 20 per cent; 



