334 



HERMANN J. MULLER 



expect all classes equal, barring differential viability, on the basis 

 of independent assortment, and approximately 50 per cent of 

 recombination between any two factors. The result was similar 

 to that obtained in the back-cross of the males (table 5) . 



TABLE 5 



WILD 

 TYPE 



females 23 



males 22 



Total 45 



BLACK BENT 



BLACK 

 BENT 



14 



23 



16 

 17 



22 

 22 



37 



33 



19 

 15 



BLACK 

 PINK 



11 

 12 



PINK 



BENT 



BLACK 

 PINK 

 BENT 



44 34 



23 



15 

 9 



10 



24 



18 



The per cents of recombinations were as follows : 



per cent 



Black-pink 54.0 



black-bent 45 . 5 



pink-bent 52.0 



Here we cannot obtain the per cents of recombinations between 

 sex and the other factors, since the parent which was heterozygous 

 for the other factors was not the one which was heterozygous for 

 sex. 



CONCLUSIONS 



The foregoing experiments prove that the gene for bent wings 

 segregates independently of the sex-linked group of genes and of 

 the two hitherto known non-sex-linked groups; accordingly, the 

 genes of Drosophila now fall into four divisions, one sex-linked, 

 corresponding to the X-chromosome, and three non-sex-linked, 

 corresponding to the three pairs of autosomes. Thus the chief gap 

 yet remaining in the series of genetic phenomena that form a par- 

 allel to the known cytological facts in Drosophila ampelophila has 

 now been filled. It may therefore be predicted that no genes 

 undergoing independent assortment of those at present known 

 can hereafter be discovered in individuals of Drosophila ampe- 

 lophila that show the chromosome configuration normal to the 

 species, and it also seems probable that when other mutations are 

 discovered in the fourth group, the genes in which they occur will 

 be found to be linked strongly to the gene for bent wings, since 



