DOMINANCE 



can become visible only in the presence of both 

 black and red, because it is a mosaic of those 

 two pigments. If the F x agouti individuals 

 are bred together they produce in the next 

 generation (F 2 ) three sorts of young, viz. 

 agouti, black, and red, which are numerically 

 as 9:3:4. This evidently is a modification of 

 the dihybrid Mendelian ratio 9:3:3:1, result- 

 ing from the fact that the last two classes are 

 superficially alike. They are red animals with 

 and without the agouti factor respectively; but 

 this agouti factor is invisible in the absence 

 of black, so that both sorts of reds look alike. 

 Together they number four in sixteen of the 

 Fo offspring. 



Fig. 35 is intended to show how the inde- 

 pendent factors behave in heredity. The black 

 parent contributes the factor B, the red par- 

 ent, R and A, so that the zygote, or nw indi- 

 vidual, contains the three factors necessary to 

 the production of agouti. When the new in- 

 dividual forms gametes (sex-cells), these will 

 l)c of four different kinds, for A is independ- 

 ent of B and of R and may pass out with 

 either one in the reduction division which sepa- 



65 



