492 - Heredity and Evolution 



50^ 



50% 



Fig. 26-15. Complete linkage: Fj male, from cross of black-vestigial and gray- 

 long, back-crossed to black-vestigial female. (Adapted from Morgan.) 



see that crossing over has occurred, because the law of segregation that the individual 



usually the members of each synapsing pair genes do not fuse, and that each gene retains 



are identical in their appearance. But the its identity without contamination by other 



genetic evidence is altogether convincing genes. But equal blocks of genes may be ex- 



and cytological corroboration has been ob- changed between the synapsing mates, as is 



tained in certain cases. It is known from indicated in Figure 26-17. The two chromo- 



