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FOUNDATIONS OF BIOLOGY 



ments. Now, assuming that the full-blooded Negro of Africa 

 bears two sets of genes for black (AABB) which are absent 

 (aabb) in the white race; then, since in the germ cells single 

 genes segregate, the cross of white and black would give only 

 a single set of genes for black (AaBb) and the hybrid (Fi) 



FiG. 144. Diagram to illustrate the results from crossing white and red flowered 

 races of Four-o'clocks ( Mirabilis jalapa) . The somatic condition (phenotype) is shown 

 graphically; the small circles represent the genes which are involved. 



would be neither black nor white, but intermediate. Again, 

 the progeny of these mulattoes, that is the F 2 and subsequent 

 generations, should show different degrees of color, as they 

 actually do, owing to varying combinations of genes; except 

 in the small number of cases of extracted dominants (black) 

 and extracted recessives (white). Therefore the intermedi- 

 ate color of the offspring of black-white crosses is reasonably 



