I20 GENETICS 



and aabbcc. Their progeny (Fi generation) would all have 

 the constitution AaBbCc. Such Fi individuals of course 

 produce a variety of germ cells, in accordance with the prin- 

 ciples that each germ cell receives one member of each pair 

 of autosomes, and that the different pairs of autosomes are 

 distributed independently. Each parent AaBbCc thus yields 

 the following 8 types of germ cells: ABC, ABc, AbC, aBC, 

 Abe, aBc, abC, abc. 



When each of the 8 kinds from one parent unites with 

 each of the 8 kinds from the other, there are produced of 

 course 64 groups, which can be arranged in a table like the 

 16 groups of table 2. If we classify the 64 individuals by 

 the characters which they manifest, we find that there are 

 8 different phaenotypes manifesting respectively the fol- 

 lowing characteristics: 



ABC, ABc, AbC, aBC, Abc, aBc, abC, and abc 



That is, some are dominant for all three characters, 

 some for a particular two and recessive for the other; some 

 are dominant for a particular one and recessive for the 

 other two; and some are recessive for all three. The differ- 

 ent phaenotypes are present in different proportions; the 

 proportions when a large number are examined are as fol- 

 lows: 



27ABC + 9ABC + 9AbC + 9aBC + 3Abc + 3aBc + 



3abC + labc 



The total number of different combinations (genotypes) 

 that occur in such a case is 27, or 3^. These combinations 

 can be obtained in their correct proportions by multiplying 

 together algebraically the expressions: 



(AA + 2Aa+aa) (BB + 2Bb + bb) 

 (CC + 2Cc + cc) 



Similar but still more complex series are obtained if 



