98 MENDELISM chap. 



and the four sorts were produced in approximately 

 equal numbers. In such a family there was no 

 special association of either of the two colour 

 varieties with one sex rather than the other. But 

 the reverse cross, F^ female by lacticolor male, gave 

 a very different result. As in the previous cross, 

 such families contained equal numbers of the normal 

 form and of the recessive variety. But all of the 

 normal grossulariata were males, while all the lacti- 

 color were females. Now this seemingly complex 

 collection of facts is readily explained if we make 

 the following three assumptions : — 



(i) The grossulariata character {G) is dominant 

 to the lacticolor character {g). This is obviously 

 justified by the experiments, for, leaving the sex 

 distribution out of account, we get the expected 

 3 : I ratio from F^ X Fj, and also the expected ratio 

 of equality when the heterozygote is crossed with 

 the recessive. 



(2) The female is heterozygous for a dominant 

 factor (^F) which is lacking in the male. The con- 

 stitution of a female is consequently Ff, and of a 

 male ff. This assumption is in harmony with the 

 fact that the sexes are produced in approximately 

 equal numbers. 



(3) There exists repulsion between the factors 

 G and i^^ in a zygote which is heterozygous for 

 them both. Such zygotes {FfGg) must always be 

 females, and on this assumption will produce gametes 

 Fg and fG in equal numbers. 



We may now construct a scheme for com- 

 parison with that on page 92 to show how these 

 assumptions explain the experimental results. The 



