472 



GENETICS 



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I 



Fig. 250. — Results of crossing a red-eyed female Drosophila with a white-eyed 

 male. The X-chromosomes are represented as carriers of the genes determining 

 eye-color. W is the symbol used for a gene for red eye-color which is dominant 

 to a gene, indicated by u, for white eye-color (c/. Fig. 257, p. 481). The hook- 

 shaped chromosome which does not contain a symbol for a gene represents the 

 Y-chromosome of the male (c/. p. 448). This cross is the reciprocal of that 



shown in Fig. 251. 



(From Morgan, et aL, "The Mechanism of Mendelian Heredity," copyright, 1922, by 

 Henry Holt and Co., reprinted by permission.) 



