676 THE PHYSIOLOGY OF REPRODUCTION 



The results are represented in the following scheme, where II 

 represents the red-eyed factor and w the white-eyed : 



(1) RR 9 x tvw g gave Rw and Rw 9- 



(red) (white) (red) (red) 



(2) Rw 9 x Rw $ gave Rw <J, ww <J, Rw ?, and RR 9. 



(red) (red) ' (red) (white) (red) (red) 



(3) Rw 9 x w^ c? gave Rw , ww; $, RMJ 9> an d ?*r 9- 



(red) (white) "(red) (white) (red) (white) 



(4) ivw 9 x Rw (J gave ?/,*w ^ and Rw 9- 

 (white) (red) (white) (red) 



(5) vnv 9 x ww <$ gave ww $ and ?? 9- 

 (white) (white) (white) (white) 



These results are to be explained on the assumption that the 

 red-eyed male produces two sorts of spermatozoa, male-producing 

 and female-producing, and that whereas the female - producing 

 spermatozoa carry the factor for red eyes, the male-producing ones 

 do not. This conclusion has received cytological confirmation in the 

 discovery of Miss Stevens 1 that the male Drosophila has a pair of 

 unequal chromosomes, and Morgan naturally assumes that the larger 

 or X chromosome carries the sex-linked characters. 



Doncaster had previously found in the currant moth, Al>i-<i.">* 

 grossulariata, a condition of things which is the precise converse of 

 what Morgan has established for Drosophila. He showed that in 

 with this insect there is a rare variety, which generally occurs only 

 in the female sex. This variety, which is called A. grosxnhrr'nitu 

 lacticolor, is a Mendelian recessive, so that when crossed with an 

 ordinary grossulariata male, the offspring are all typical, the hu-ticol&r 

 variety disappearing. Experimental crossings yielded the following 

 results : 



(1) Lact. 9 x gross. <J gave males and females all gross. 



(2) Heterozygous 9 x heterozygous ^ gave gross. <, gross. 9> 



and lact. 9- 



(3) Lact. 9 x heterozygous ^ gave all four possible forms 



(gross. (J, lact. ^, gross. 9, and lact. 9) tn e lacticolor males 

 being the first ever seen. 



(4) Heterozygous 9 x lact. ^ gave gross. ^ and lact. 9- 



(5) Lact. 9 x lact. gave lact. and lact. 9- 



(6) Wild gross. 9 x lact. gave gross. ^ and lact. 9- 



It is shown, therefore, that males of the lacticolor variety can be 

 produced by mating lacticolor females with heterozygous males (i.e. 

 with males obtained by crossing the two original varieties, and so 

 presumably bearing two sorts of gametes), but that the converse 



! Stevens, ' A Study of the Germ Cells of Certain Diptera." ./</'/-. /;'.>/>. /<i/., 

 vol. v., 1908. 



