LINKAGE GROUPS 89 



In the chromosome group of Drosophila melano- 

 gaster {fig. 39) there are four pairs of chromosomes, 

 three of nearly the same size and one much smaller. 

 Xot only is there agreement between the number of 

 hereditary groups and the number of the chromo- 



FEMALE MALE 



IV / r 



Fig. 39. — Female group and male group of 

 chromosomes of Drosophila melanogaster. 



somes, but even the size relations are the same, for 

 there are three large groups of characters and three 

 pairs of large chromosomes, and one small group of 

 characters and one pair of small chromosomes. 



The Four Linkage Groups of Drosophila 



Melanogaster 



The following description of the characters of the 

 wild fly may be useful in connection with the account 

 of the modifications of these characters that appear 

 in the mutants. 



The head and thorax of the wild fly are grayish- 

 yellowy the abdomen is banded w4th alternate stripes 

 of yellow and black. In the male {fig. 6, left) , there 

 are three narrow^ bands and a black tip. In the female 



