X0.5S3] BOLE OF EXYIBOXMEXT IX DEOXOPIIILA 403 



linked with yellow and with white. The F, YWN son of 

 the original YWN female must have come from the other 

 sex chromosome of the YWN female— the one that did 

 not carry the lethal. The count of the males in the F 2 

 gives both in B and in C a 2:1 ratio which is the charac- 

 teristic ratio for a sex-linked lethal. The reciprocal cross 

 was also made, but only twice; the Fo counts are given 

 in Table IX. 



Parents: GRAb <j> by YWN^ 

 P,: GRX$ (or slightly Ab) — GRAb <$ 



The expected gametes of the Y 1 female are the same, of 

 course, as before, but the male contains all three sex- 

 linked dominant factors, GKAb. Consequently in V half 

 of the GRAb female class is pure and half is heterozygous 

 for abnormality. The GRAb F 2 males, on the other hand, 

 are all pure, in the sense that they have only one factor 

 for abnormal and no factor for normal. It is probable 

 that most of them here are phenotypically abnormal. 



The relation of the non-cross-over and the cross-over 

 gametes is the same as in the reciprocal cross, since only 

 sex-linked factors are involved, but the cross-over r!a— e- 

 given in Table IX are different in the female classes in so 

 far as the female producing sperms, that carry GRAb, 

 contain three dominants. In one of the two counts given 

 in the table the cross-over class that has changed to 

 phenotypic normal is relatively large; in the other count 

 it is small. 



Gray, White, Abnormal by Yellow, Red, Normal 

 The next largest series of experiments involves the same 

 three pairs of characters but combined in a different way. 

 The results are shown in Table X. Diagram, IV shows 

 the relative positions of the factors in this combination. 



