Two Sex-limited Characters. 
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The method of inheritance of two sex-limited characters in 
the same animal. 
By T. H. MORGAN. 
[From the Department of Zoology, Columbia University.] 
At the last meeting of the society I reported the occurrence 
of a white-eyed mutant in a pedigree culture of the fly Drosophila 
ampelophila. The mutant bred to his red-eyed sisters produced 
1,237 red-eyed (male and female) and 3 white-eyed (male) in- 
dividuals. This sporadic occurrence within the strain is due to 
further sporting in the eggs of certain females. The same strain 
has continued to produce white-eyed mutants and these are 
always of the male sex. 
This white-eyed condition has shown itself to be sex limited 
in its inheritance, i. e., in certain combinations the character is 
transferred to one sex only. For instance — If a white-eyed male 
is bred to a red-eyed individual all of the offspring are red-eyed 
(males and females). These inbred produce red-eyed males and 
females and white-eyed males. The reds are to the whites as 3 to 1 . 
Thus half of the grandsons inherit the new character but none of 
the granddaughters. 
This result can be explained by means of a very simple hypoth- 
esis. If R = red eyes; W = white eyes, and X = the sex factor 
(one X being a male and XX a female) ; then the red female fly 
will be RXRX and her eggs RX and RX ; the white male will be 
WXW and his two classes of spermatozoa WX and W. When 
crossed the following combinations result. 
RX-RX 
wx-w 
RXWX-RXW 
red female red male 
When these individuals are paired the outcome is shown by the 
following formulae: 
RX-WX 
rx-w 
RXRX =red female 
RXWX =red female 
RXW=red male 
WXW = white male 
