184 JOHN S. DEXTER. 



and flies with a yellow body and white eyes; both stocks were 

 sent to me by Morgan. The origin of these mutations, and the 

 facts of their individual inheritance, have been described by 

 Morgan 1 in earlier papers. 



In speaking of the flies from this time on, I shall use the letter 

 N to signify the presence of the factor for normal body color, 

 Y for yellow body color, R for red eye, and W for white eye. 

 Of these factors, N is dominant over F, and R over W. The 

 factors N and R are only found in association with the X- 

 chromosomes, which is duplex in the female but simplex in the 

 male. This means, of course, that N and R, as used here, are 

 sex-linked characters. It is not necessary to assume that any 

 of these factors are units but that they act as units in the following 

 experiments. 



According to the theory to be tested we have the following 

 data as to the gametic constitution of the flies. A pure NR 

 female has the constitution NRX NRX, and all her gametes 

 bear the factors, NRX. A pure NR male has the constitu- 

 tion NRX YW, and the sperms bear either of two combinations 

 of factors, NRX or YW. A pure YW female has the consti- 

 tution YWX YWX; the gametes all bear YWX. The pure 

 YW male has the constitution YWX YW, and his gametes bear 

 either YWX or YW. 



EXPERIMENT I. 



In experiment I, a pure NR female was crossed to a pure YW 

 male. The results to be expected in the F\ and F 2 generations 

 if eye color and body color are independently mendelizing, are 



shown in Table I. 



TABLE I. 



Pi. NRX NRX = NR 9 YWXYW = YWtf 



Gametes NRX YWX, YW 



Fi. NRX YWX = NR9 NRXYW = NR<? 



Gametes (i) NRX, (2) YWX, NRX, YW 



(3) YRX, (4) NWX 



F 2 . NRXNRX=NR9 NRXYW=NRc? 



YWX NRX = NR9 YWXYW = YWtf 



YRX NRX = NR9 YRX YW = YRtf 



NWX NRX = NR 9 NWXYW = NW<? 



1 Science, July 22, 1910, p. 120; Science, March 31, 1911, p. 496; Jour. Exper. 

 Zoo/., November, 1911, p. 365. 



