382 



CHARACTER EXPRESSION OF GENES 



eration into red and white or red and cherry, as the case 

 may be. A white-eyed fly crossed to a cherry-eyed fly 

 similarly gives white and cherry in the second generation. 

 Since any two of these genes (red, cherry, white and also 

 eosin) for eye-color may pair with one another they must 



B*d Bal« 



WTii 



I \ ^ < / • \ 



t« f«naT«-^ ^ «(hit« male 



I \ 



I \ 

 Chtrry fwnal^A''^ -«» Cherry ■*!• \ 



M / 



/ / \ / 



^\ 'I . / 



Ch«rr/f«m«lt Chtrry ■•!•' 



Fio. 113. — Multiple Allelomorphs. Cherry is a modification of 

 the same red gene which when modified in another way produces 

 white eyes. It is also known to undergo still another mut-ation which 

 gives rise to eosin eyes. The dijigram shows the l^ehavior of the sex 

 chromosomes in which these genes are contained in the two crosses 

 white female by cherry male and cherry female by red male. They 

 should be compared with the cross between a whit« female and a red 

 male in the last chapter. From an examination of these diagrams 

 it will be observed that any two of these genes will pair with one 

 another because they all occupy the same relative position in their 

 respective chromosomes. Such a syst^^m of several genes able to 

 pair with one another constitutes a system of multiple allelomorphs. 



