MASKED CHARACTERS 205 



case of two pairs of allelomorphs described on p. 187. 

 We may write A foi presence of grey pigment, a for 

 absence of grey pigment, B for presence of purple, and 

 b for its absence. Then the original cross was of the 

 form Ab xaB, from which AaBb resulted in F r And 

 the visible characters of the types which appeared 

 in F 2 would be represented by $AB + 3Ab + (3&B + 

 iab). On referring to the account given on p. 187 it 

 will be seen that one in nine of the purple plants is of 

 the constitution ABAB t and may be expected to 

 breed true. 



A precisely similar result may be obtained in F 2 in 

 cases where there is no reversion in F r In the 

 following example a white pea, which did not contain 

 the masked purple factor, was crossed with a ' maple- 

 seeded ' pea. The characteristic feature of maple is a 

 marbling oi brown spots on a grey ground colour. In 

 Fj the marbling was dominant, and the seeds resembled 

 the maple parent. 



In F 2 there appeared 9 maple : 3 grey : 4 white 

 i.e., the same ratio as in the previous case, this time 

 without reversion. This ratio is brought about by the 

 simple combinations of two pairs of allelomorphs A -a, 

 and C-c, C being unable to manifest itself unless A is 

 present in the same zygote. As a matter of fact, in 

 this particular case C does sometimes just manage 

 to appear in the absence of A, the result being a 

 white seed with a sort of faint ' ghost ' of a maple 

 marking. 



When a strain bearing both maple marking and 

 purple spots is crossed with a white in which neither 

 of these factors is latent, we can easily calculate the 



