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 

 F 2 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 new indi- 

 vidual, contains the three factors necessary to 

 the production of agouti. When the new in- 

 dividual forms gametes (sex-cells), these will 

 be 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 



