MENDEL'S FIRST LAW 



31 



Black is accordingly treated as a recessive in nearly 

 all experiments. 



a' 



Fig. 7. — Normal eye, a, o', heterozygous eye 6, V , and bar eye c, c', of the vinegar flj'. 



A mutant eye shape of Drosophila, called *^bar'* (Fig- 

 7, c) has an intermediate hybrid type (Fig. 7, &). The Fg 

 group may be represented (Fig. 8) in the following scheme : 



FiQ. 8. — Relation of bar eye to normal eye, as shown by the Fi classes. 



In this case the hybrid, intermediate type, overlaps the 

 bar type, so that in Fr these two latter types give a nearly 

 continuous class. At the other end of the F2 series, the 

 round eyed normal (or wild) type can be distinguished 

 without difficulty from either of the other classes. Bar is 

 therefore normally treated as a dominant. 



