368 



LINKAGE PHENOMENA 



be the case if the experiment concerned independent char- 

 acters (Fig. 106). Although Gray Long x black vestigial 

 and Gray vestigial x black Long give identical first gen- 



Fio. 105. — Illustrating the Behavior of Linked Characters in the 

 vinegar fly. A black-bodied fly A-ith vestigial wings is mated to a 

 gray-bodied fly with long wings. The first hybrid generation is long- 

 winged and gray-bodied. When this is bred to a black vestigial fly 

 (i.e. back-crossed to the double recessive type) the grandparental 

 types appear in the second hybrid generation. In the chromosome 

 diagrams the gene 6 for black body is contained in the same chromo- 

 some with the gene v for vestigial wings so that the two remain 

 linked together throughout all the cell divisions of growth and 

 through the reduction divisions which produce the gametes, and 

 therefore reappear together again in the second hybrid generation. 

 The .same is al.so, of course, true for the dominant genes B for gray 

 body and V for long wings. 

 Morgan, The Physical Basis of Heredity. Lippincott. 



