64 



MORGAN 



2,459 red-eyed females, 

 1,011 red-eyed males, 

 782 white-eyed males. 



No white-eyed females appeared. 

 The new character showed itself 

 therefore to be sex limited in the sense 

 that it was transmitted only to the 

 grandsons. But that the character is not 

 incompatible with femaleness is shown 

 by the following experiment. 



The white-eyed male (mutant) was 

 later crossed with some of his daugh- 

 ters (Fi), and produced: 



129 red-eyed females, 

 132 red-eyed males, 

 88 white-eyed females, 

 86 white-eyed males. 



The results show that the new char- 

 acter, white eves, can be carried over 

 to the females by a suitable cross, and 

 is in consequence in this sense not 

 limited to one sex. It will be noted that 

 the four classes of individuals occur 

 in approximately equal numbers (25 

 per cent.). 



An Hypothesis to Account for the 

 Results.— The results just described can 

 be accounted for by the following 

 hypothesis. Assume that all of the 

 spermatozoa of the white-eyed male 

 carrv the "factor" for white eyes 

 "W"; that half of the spermatozoa 

 carrv a sex factor "X," the other half 

 lack it, /'. e., the male is heterozvgous 

 for sex. Thus the symbol for the male 

 is "WWX," and for his two kinds of 

 spermatozoa WX— W. 



Assume that all of the eggs of the 

 red-eyed female carry the red-eyed 

 "factor" R; and that all of the eggs 

 (after reduction) carrv one X each, 

 the svmbol for the red-eved female 

 will be therefore RRXX and that for 

 her eggs will be RX— RX. 



When the white-eyed male (sport) 

 is crossed with his red-eyed sisters, the 

 following combinations result: 



WX-W(male) 

 RX-RX (female) 



RWXX (50%) 

 Red female 



RWX(50%) 

 Red male 



When these Fi individuals are 

 mated, the following table shows the 

 expected combinations that result: 



It will be seen from the last formulae 

 that the outcome is Adendelian in the 

 sense that there are three reds to one 

 white. But it is also apparent that all 

 of the whites are confined to the male 

 sex. 



It will also be noted that there are 

 two classes of red females— one pure 

 RRXX and one hybrid RWXX-but 

 only one class of red males (RWX). 

 This point will be taken up later. In 

 order to obtain these results it is neces- 

 sary to assume, as in the last scheme, 

 that, when the two classes of the sper- 

 matozoa are formed in the Fi red male 

 (RWX), R and X go together— other- 

 wise the results will not follow (with 

 the s\'mbolism here used). This all-im- 

 portant point can not be fullv dis- 

 cussed in this communication. 



The hypothesis just utilized to ex- 

 plain these results first obtained can be 

 tested in several wavs. 



VERIFICATION OF HYPOTHESIS 



First Verification.— U the svmbol for 

 the \\'hite male is WWX, and for the 

 white female WWXX, the germ cells 

 will be WX-W (male) and WX-WX 

 (female), respectively. Mated, these 

 individuals should give 



WX 

 WX 



W(male) 

 WX( female) 



WWXX (50%) 

 White female 



WWX (50%) 

 White male 



