50 THE THEORY OF THE GENE 



chromosomes onlv a few such flies survive. The occur- 

 rence, however, of such recessive eyeless flies in the first 

 generation corroborates the interpretation that the eye- 

 less gene is carried by chromosome-IV. 



The same results are obtained when the two other 

 mutant genes, bent and shaven, are used in a similar 



Trip 1 0-12: 



Haplo-IY 



Fig. 32. 

 Haplo-IV and triplo-IV of D. melanogaster. The chromosome 

 groups are represented, respectively, above to the left, and to the 

 right of the figures. 



experiment, but the proportion of recessive flies that 

 hatch in Fi is still smaller, indicating that these genes 

 have an even greater weakening effect than the eyeless 

 gene. 



Occasionally flies arise in which three chromosome- 

 IV 's are present. These are triplo-IV 's (Fig. 32). They 

 also differ from the wild type in several, or many, per- 

 haps in all their characters. The eyes are smaller, the 

 body color is darker, and the wings are narrower. If a 



