CIL\PTER V 



INHERITANCE OF QUANTITATIVE 

 CHARACTERS 



This phase of the factor hypothesis, if true, is of 

 fundamental importance, not only to genetics but to 

 general biology. It is based upon the conception of 

 cumulative factors, and as it is presented it will be real- 

 ized that it throws light not only upon numerous breed- 

 ing problems, but also upon variation in general, which 

 means evolution also. A cumulative factor may be de- 

 fined as one which, when added to another similar factor, 

 affects the degree of development of a character. 



It will be recalled that Correns crossed red and white 

 strains of Mirahilis and obtained pink hybrids. The 

 suggested explanation of this result was that a single 

 dose of the red determiner gives pink while a double 

 dose gives red. When Correns inbred these pink 

 hybrids, he obtained the result presented in fig. 8, that 

 is, I red 12 pink:i white. The mechanism in this case 

 is quite evident. 



With this diagram in mind we shall consider some of 

 the experiments of Nilsson-Ehle (6, 7) at the Swedish 

 Experiment Station. He crossed two strains of wheat 

 with red and white kernels. The Fj individuals had light 

 red kernels, which of course suggests a repetition of the 

 situation shown by Mirahilis in the experiment of Cor- 

 rens. The F2 generation, however, showed a very dif- 

 ferent result. The reds and whites appeared in the 



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