ARCHITECTURE OF THE GERMPLASM 239 



crosses of this kind, Morgan obtained 41.5% each of 

 gray-long and black-vestigial and 8.5% each of 



'Parents 



Gametes 



Gametes 



FIG. 70. Typical linkage in Drosophila. Reciprocal to the case 

 shown in Fig. 69. Data from Morgan. 



the new combinations of black-long and gray-vestigial. 

 (See Figure 71.) The new combinations represent 

 cross-overs or breaks in the linkage of the genes within 

 the chromosomes. 



Although this superficially resembles the free assort- 

 ment or segregation of typical Mendelian crosses, it 



