112 



GENETICS IN RELATION TO AGRICULTURE 



trated by the cross yellow white female by gray red male. The genetic 

 formula of a yellow white female is (ywX)(ywX), and of a gray red 

 male (YWX)Y. In these formulae y stands for the factor for yellow 

 body-color and w for white eye-color, and the capital letters for the corre- 

 sponding dominant allelomorphs present in the wild type. When two 

 such flies are bred together the FI consists of females of the genetic con- 

 stitution (YWX)(ywX) and males of the genetic constitution (ywX)Y. 

 The Fi females, therefore, have gray bodies and red eyes and the males 

 have yellow bodies and white eyes. Gray red females of the genetic 

 constitution (YWX)(ywX} produce four kinds of eggs in the following 

 proportions : 



(YWX) 49.45 per cent. (ywX) 49.45 per cent. 

 98.9 per cent, non-cross-over gametes. 



(YwX) 0.55 per cent. (yWX) 0.55 per cent. 

 1.1 per cent, cross-over gametes. 



When such a female is bred to a yellow white male, genetic constitu- 

 tion (ywX) Y, which produces only two kinds of sperms, (ywX) and Y, 

 the progeny in both sexes obviously will be in the ratio 



49.45 gray red: 49.45 yellow white: 0.55 gray white: 0.55 yellow red. 

 Table XXI shows the results which have been secured, mostly from matings 

 of this type. 



The relations shown when the factors enter in the reverse combinations 

 may be determined by mating a gray white female, genetic constitution 

 (YwX) (YwX) to a yellow red male, genetic constitution (yWX)Y. 

 This gives F\ gray red females of the constitution (YwX)(yWX), and 

 gray white males of the genetic constitution (YwX)Y. In this case 

 the FI females produce four kinds of eggs in the following proportions: 



(YwX) 49.45 per cent. : (yWX) 49.45 per cent. 

 98.9 per cent, non-cross-ever gametes. 



(YWX) 0.55 per cent. : (ywX) 0.55 per cent. 

 1.1 p?r cent, cross-over gametes. 



TABLE XXI. FACTOR LINKAGE IN GRAY RED FEMALE DROSOPHILAS OF THE TYPE 



(YWX)(ywX) 



