HEREDITY AND VARIATION 



factors, or genes. Mendel proved that a factor related to a specific expression 

 of a character, such as dwarf stem, was not altered by association with a factor 

 for the alternate expression of that character, such as long stem. Hereditary 

 factors for the alternate or allelomorphic states in which characters are found 

 to exist retain their unmodified independence even when present together in 



Females 



Males 



Fig. 6.9. 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 the gene for red eye color which is dominant to the gene, indicated by w, for white 

 eye color (cf. Fig. 6.17). The hook-shaped chromosome which does not contain a symbol for a 

 gene represents the Y-chromosome of the male (cf. p. 209). This cross is the reciprocal of 



that shown in Fig. 6.10. (Modified from T. H. Morgan et ai, The Mechanism of Mendelian 



Heredity, copyright 1922 by Henry Holt and Co., printed by permission.) 



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