INDEPENDENT MENDELIAN INHERITANCE 



91 



The FI hydrid ZzRrli was the normal flower form and produced 

 blossoms of a magenta coloration, i.e., red on ivory. From self-fertilized 

 seed of such plants there were produced 124 plants distributed with 

 respect to their phenotypes as shown in Table XIII. For so small a popu- 

 lation, in number of individuals only about twice that necessary to obtain 

 a triple recessive, the agreement is good. 



To account for these hybrid results on a chromosome basis it is 

 necessary to assume merely that the three pairs of allelomorphs are borne 

 in different pairs of chromosomes. When germ cells are formed in the FI 



FIG. 45. Diagrammatic representation of reduction divisions in an FI snapdragon of the 



genetic constitution ZzRrli. 



hybrids the members of the three pairs of chromosomes separate independ- 

 ently so that eight different kinds of gametes are formed. In Fig. 45 are 

 shown diagrammatically the reduction divisions in an FI snapdragon of 

 the genetic constitution ZzRrli. Since any one of these types of re- 

 duction has a good as chance of occurrence as any other one, the eight 

 kinds of gametes are produced in substantially equal numbers. When 

 such a plant is self-fertilized there are 64 possible combinations as shown 

 in the checkerboard in Fig. 46. In the description of phenotypes in this 

 checkerboard certain differences between homozygous and heterozygous 

 forms have been disregarded. This is true particularly for the Rr 

 individuals as contrasted with the homozygous RR individuals. The 



