This belief is based on the fact that the color of the F2 

 (offspring of mulattoes) is much more variable than that of 

 Fi, and on the fact that white and black appear in the F2 

 generation, breeding true to their respective color. 



3 — Compound Factors 



Some of the most complex cases of Mendelian inheri- 

 tance occur when certain determiners interfere with the 

 actions of others, or do not act unless aided by others. 



Four types of such compound determiners have been 

 observed : — 



(a) The Complementary type where the two unlike de- 

 terminers become separated in breeding, and the character 

 disappears, reappearing when the two determiners are again 

 brought together. Examples of this type are Bateson's 

 White Sweet Peas (Emily Henderson), East's purple 

 maize, and Combs of fowls. 



''Emily Henderson''' Sweet Peas. — Bateson crossed two 

 strains of this variety and there appeared purples. When 

 these Fi purples were selfed the progeny consists of whites 

 and purples in the ratio of 7 to 9. This case of reversion ex- 

 plains the appearance of individuals with colored flowers of 

 different types among the descendants of two white sweet 

 peas of separate strains. The results are explained on the 

 following assumption: — 



C = Factor for color production (sensitizer). 



c = Absence of factor for color production. 



P = Factor for purple (basis). 



p = Absence of factor for purple. 



Only when the factors C and P come together will the 

 purple color be produced. 



(1) Hybrids of white varieties in the Fi generation 

 will have the formula CcPp — purple. 



(2). Hybrids of the F2 generation: 



CP Cp cP cp = male 



gametes 



f CP 



Female 

 Gametes \ 



Cp 

 cP 

 cp 



Phenotypically 9 purple and 7 white. 



1U4 



