HERITAGE OF THE INDIVIDUAL 



285 



explained, if we regard the character black as the expression 

 of at least two pairs of genes, neither of which alone gives 

 black but only when reinforced by the other. The infrequent 

 appearance of pure whites or blacks in the F 2 and later gen- 

 erations is not due to lack of segregation, but to the fact that, 

 since the parental characters have a multiple gene basis, the 

 chances are slight that in segregation all the separate genes 



AB Ab a B a b 



A B 



A b 



a B 



a b 



FIG. 145. Recombination square showing the result of mating two 

 mulattoes, each having the color factors AB and their absence ab the latter 

 from their respective white parents. The color of the offspring varies from 

 black (upper left corner) to white (lower right corner). Compare Fig. 140. 

 (After Conklin.) 



will be brought together in a single gamete and further 

 that such a gamete at fertilization will meet one similarly 

 endowed. (Fig. 145.) 



From experiments with several races of Locusts which 

 breed true for color pattern, it has been found that the hy- 

 brids between any two show the entire pattern of each parent, 

 one superimposed upon the other. Thus, again merely by 

 inspection, it is possible to determine the parental compo- 

 nents, and since such hybrids give progeny showing the 

 1:2:1 ratio, it is evident that the mosaic, instead of blended, 

 result is due merely to the fact that each of the 'alternative' 

 characters completely expresses itself. 



