Crossing-over 



I^T 



^J 



O 



?t 



Fi$ 



yellow 

 white 



y^ 



99<^c 



l<^c 



Fig. 8o. Crossing-over Shown in a Reciprocal Cross 



If a female with white eyes and gray wings is crossed with a male having 

 red eyes and yellow wings, the offspring will be dominant for both char- 

 acters, that is, have the wild type appearance (left in F^). If such a hy- 

 brid female is mated with a double recessive male, four kinds of flies will be 

 produced in the F^ generation. Again, in 99% the two characters that 

 went in together come out together, showing linkage; but in 1% the com- 

 bination is reversed, showing that linkage is not entirely perfect. From 

 Morgan, The Theory of the Gene, published by Yale University Press. 



