SEX-LINKED CHARACTERS IN DROSOPHILA. 185 



This table shows that all members of the F! generation should 

 have the appearance of normal NR's. In my experiments, this 

 was true without exception. 



The females of the FI generation should produce four classes 

 of eggs, representing all combinations of N, R, Y and W. The 

 males should produce sperms of two classes. The combination 

 of these gametes should produce in the F 2 generation equal 

 numbers of males and females, but all of the females should be 

 NR, while one fourth of the males should belong to each of the 

 following classes: NR, YW, YR, NW. 



If, on the contrary, the N and R are completely coupled we have 

 the same result in the FI generation, but the gametes of the FI 

 females would be of two classes only, viz., NRX and YWX, 

 while those represented in the table by (3) and (4) would be 

 absent. Therefore there would occur in the F 2 generation NR 

 females as before, and only two kinds of males, one half being 

 NR and the other half YW. 



Table II. shows the actual results of this experiment. From 

 24 bottles I raised 11,394 flies. Of these 6,08 1 were females. 

 All but one of these females were NR. The other was NR 

 on the left side and YW on the right, and may be for present 

 purposes ignored 1 as an anomaly. Of the males there were of 

 class NR, 2,870; class YR, 34; class NW, 36; class YW, 2,373. 

 Whatever the explanation may be, it is obvious that coupling 

 has occurred. It is equally obvious that the coupling is not 

 complete. 



The result for the individual bottles accorded with that of 

 the total. There is in every bottle except number 6, a larger 

 number of NR males than of YW males. This is without 

 doubt due to a greater vitality in the normal flies than in the 

 mutants, for also in the pure cultures the normal flies are much 

 more fertile than the others. This matter is discussed by Morgan 

 in one of the papers mentioned 2 above, under the heading, " The 

 Fertility of Deficient Mutations." I have no reason to dissent 

 from the statements made there. The reasons for this infer- 



1 This fly was active and except for color appeared to be normal. I attempted 

 to mate her to YW males, but she appeared to be sterile, and after two weeks 

 she was preserved for histological study. 



2 Jour. Exper. Zoo/., Nov., 1911. 



