CHAPTER VIII 

 NEO-MENDELISM (Continued] 



6. TRUE-BREEDING HYBRIDS. This situation was 

 referred to in chapter v, but comes up again in the 

 present context. The statement was made that a num- 

 ber of practical breeders had reported that by crossing 

 distinct races they had not only obtained hybrids inter- 

 mediate with regard to one or more characters, but also 

 that these hybrids when inbred continued to breed true 

 to their intermediate condition and that the original 

 parent races never reappeared. 



One explanation of this situation offered by geneti- 

 cists was that where a great many factors are involved 

 it is practically a mathematical impossibility for either 

 of the parent races to reappear, for the chances would be 

 overwhelmingly against the exact coming together of the 

 exact combination of factors. This explanation should 

 be considered a little more fully in the light of what has 

 been stated concerning cumulative factors. 



Suppose that CORRENS in crossing the red and white 

 races of Mirabilis had been dealing, not with one factor 

 determining redness, but with six, the red color being 

 determined by six different factors, cumulative in their 

 effect but separately inherited. With only two cumu- 

 lative factors the F 2 situation is represented by fig. 15, 

 where it is evident that one individual of each parent 

 type appears in 16 of the F 2 individuals. This ratio 



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