64 



INBKEEDING AND OUTBREEDING 



Individuals of Fj 

 Gray Long 



Gametes of Femal 

 Direct sgregates Cr^sovere 



Gametes of Male 



All direct segregates 



Double recessive 



black vestigial 



used \n back crosses 



Gray 



vestigial vestigial 

 S% 



black 

 Ixs ng; 

 50.0^ 



Cray 



vestigial 

 50.0JS 



FIG. 21. Diagram to illustrate linkage breaks 'or "crossing-over" between the loci 

 containing the factors for the allelomorphic pairs. Gray body, black body and long wing 

 vestigial wing in Drosophila. (After Morgan.) 



A complete visualization of this series of matings is 

 given in Fig. 21. 



