Some Apparent Exceptions 91 



AA, BB, C, E, U, etc., are all formulae for the 

 factors present in gray rabbits. In fact, there 

 may be thirty-two aU-over gray rabbits that 

 differ in the complex of factors present in their 

 body cells. They appear similar, and are 

 therefore said to be phenotypically alike; but 

 they all may give unlike progeny, since their 

 germ ceUs, eggs and sperm, will contain unlike 

 assortments of factors, and they are therefore 

 caUed genotypically unlike. 



If we are crossing two individuals that differ 

 in one factor (or one character, if that character 

 is determined by a single factor), the ratio of 

 individuals in the F^ generations is 3 to i, in 

 which 3 possess the factor in question, one does 

 not. Of the three, one has it in double dose, 

 two in single dose. There are two phenotypes 

 in this case, i.e., two differently appearing 

 animals or plants, and three genotypes. If two 

 factors are involved, the proportion is 9-3-3-1, 

 that is (3 + I)^ A reference to the checker- 

 board (p. 43) showing possible combinations 

 in the F^ generation in this case shows there are 

 four phenotypes (2") and nine genotypes (3'). 



