64 Outline of Genetics 



(Any such mass of fractions is readily handled on the black- 

 board or scratch pad by considering the C, R, and P ratios under 

 separate columns, and scratching out fractions as they are dis- 

 posed of by being carried on. At the end, if the procedure has 

 been orderly, the proper fractions will be found under the proper 

 columns.) 



Other methods of solving these problems could be worked out. 

 All that is necessary in any method is clear vision of the Mendelian 

 mechanism, analysis into monohybrid components and separate 

 solution of each, followed by an orderly synthesis, the method of 

 synthesis always being indicated by the nature of the factors with 

 which one deals. 



As before, the physiological mechanism accounting for the 

 behavior of the P factor has been only guessed at. It has been 

 found that the purple pigment is produced by the same substance 

 as the red, but represents a higher state of oxidation, which sug- 

 gests the following possibility. C is oxidized by 7? up to a certain 

 point, where red is produced; P, an additional enzyme, is capable 

 of oxidizing the red pigment still further to purple. P is incapable 

 of attacking the original chromogen, but when R carries the 

 attack to a certain point, P can function and carry the oxidization 

 further. As a consequence, P without R gives white grains, while 

 R gives red grains only in the absence of P. 



3. Inhibitory factors. — ^An inhibitory factor pre- 

 vents the action of some other determiner or factor. 

 This factor type also can be illustrated in connection 

 with inheritance of grain color in corn (East 3). If one 

 were to cross a purple-grained race of corn, having the 

 formula PFRRCC, with any white-grained race, he would 

 expect all of the Fi generation to be purple. In this 

 case, every gamete produced by the purple parent would 

 have the formula PRC. As a consequence, no matter 

 what might be the formula of the white parent, every 

 Fi individual would have to have at least one dose of 

 P, R, and C, and this in itself should be sufficient to 



