LINKAGE 



379 



able number of plants and animals, and are especially well known in 

 the case of the fruit fly, Drosophila melanogaster, owing to the exhaustive 

 researches of Morgan and his coworkers. 



A Typical Case of Linkage. As a typical example may be taken the 

 following case of linkage in Drosophila (Fig. 145). A male fly with white 

 eyes and yellow body is mated to a female with red eyes and gray body. 



LINKAGE IN DROSOPHILA 



99% 



1% 



FIG. 145. Linkage in Drosophila. Red eyes in black; gray bodies stippled; white eyes 



and yellow bodies unshaded. 



The flies of the FI generation all have red eyes and gray bodies, since red 

 is dominant over its allelomorph white, and gray is dominant over its 

 allelomorph yellow. If, r now, the females of this generation are "back- 

 crossed" to males with both of the recessive characters, 1 white and yellow, 



1 This back-crossing to the pure recessive is the common method of testing the 

 genotypic constitution of hybrids. 



