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 tin- 

 following case of linkage in Drosophila (Fig. 1 15). A male fly with white 

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



linkage: in drosophila 



<M 



s 



99% 



1% 



L 



Fig. 145.-Linkage in DrosophUa. Red eyes in black; gray bodiea stippled; *hit 



and yellow bodies unshaded. 



The flies of the F 1 generation all have red eyes and .may bodies, since red 

 is dominant over its allelomorph while, and may Is dominanl 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, 

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

 genotypic constitution of hybrids. 



