GENETIC SYSTEM: RELATION TO CHARACTERISTICS I19 



gotes for both pairs of genes. The four homozygotes are 

 diverse in their combinations and in the characters they 

 manifest. They form in table 2 the diagonal from upper 

 left to lower right. Any one of these when self-fertilized or 

 mated with another like itself breeds true; that is, it pro- 

 duces offspring that have the same constitution as the par- 

 ents. 



2. Four out of the 16, or one-fourth of all the zygotes, 

 are heterozygotes for both pairs of characters. They form 

 the class numbered (5), and constitute in table 2 the diag- 

 onal from upper right to lower left. Any of these when self- 

 fertilized or mated with another like itself gives again the 

 nine different types, in the proportions above set forth. 



3. The remaining 8 in table 2, or one-half of all the 

 zygotes, are homozygotes for one of the two pairs, hetero- 

 zygotes for the other. Four are homozygotic for A and 

 heterozygotic for B; the other four are heterozygotic for 

 A and homozygotic for B. In these 8 there are but 4 diverse 

 combinations or genotypes, since in table 2, two of each 

 kind are alike. These 4 are numbered above (6), (7), (8), 

 and (9). 



If any one of these is self-fertilized. It yields 3 diverse 

 types with respect to the pair for which It is heterozygotic. 

 Thus, the class (6), having the constitution AABb, yields 

 when self-fertilized three combinations In the following 

 proportions : 



AABB +2 AABb + AAbb 



The above relations hold for all cases in which two 

 pairs of characteristics are dependent on differences In two 

 different pairs of autosomes, whatever the method of desig- 

 nating the characters or chromosomes. 



In a similar way, two parents may differ in three charac- 

 ters that are dependent on three different pairs of auto- 

 somes. Such parents could be represented as AABBCC 



