284, HEREDITY AND ENVIRONMENT 



two mulattoes, the father having 36 per cent, 

 and the mother 30 per cent, of black, ranged 

 only from 27 per cent, to 39 per cent, of black. 



Such variations in color in the F2 and in 

 subsequent generations are exactly what one 

 would expect in a Mendelian character in 

 which more than one factor is involved, as for 

 example in the case of the color of the sweet 

 peas shown in Fig. 55. Davenport, who has 

 made an extensive study of this case, con- 

 cludes that "there are two double factors 

 {AA, BB) for black pigmentation in the full 

 blooded negro of the west coast of Africa, and 

 these are separably inheritable." These fac- 

 tors are lacking in white persons (this being 

 indicated by the formula aa, bb). Since the 

 germ cells carry only single factors and not 

 double ones the cross between negro and white 

 would have only one set of these factors for 

 black color, as shown by the formula AB x ab 

 = ABab; hence the color of the Fi generation 

 is intermediate between that of the two par- 

 ents. In the F2 generation there should be a 

 variety of colors ranging all the way from 

 white to black, though pure white or pure black 



