TYPES OF MENDELIAN HEREDITY 



29 



the heterozygous condition; it is not possible to 

 produce a pure breeding race of Andakisians, for the 

 combination that produced an Andalusian falls apart 

 in the germ cells of the Andalusiaii birds. The bird is 

 blue because the pigment is not spread evenly over 

 the feather but is restricted to small but black specks. 



b' 



Fi<i. 15. — Normal (a, a') and bar eye (6, h') of Drosophila; shown in 

 side view, and as seen from above. 



The Andalusian blue is a mosaic of black and white, 

 and not at all a dilute black. 



A good example of an intermediate hybrid is found 

 when the mutant fly with bar eye (Fig. 15) is bred to a 

 wild fiy. The daughters have bar eyes that are not 

 as narrow as those of the pure bar stock. The range 

 of variation is great, however, for some of the hybrids 

 have eyes that are nearly as round as the normal, and 



