CROSSING OVER 



89 



Fia. 36. — Back-cross of Fi female (out of black vestigial by wild) to black vestigial male. 



in the same chromosome, or whether they enter the cross 

 in opposite chromosomes — their likelihood of interchange 

 is exactly the same. If the F^ male had been back-crossed 

 (Fig. 34) only two kinds of offspring would have been 



