58 



S. J. HOLMES AND H. M. LOOMIS. 



It may be seen that in crosses of black and black that many 

 cases of lighter hair make their appearance, a result that might 

 be explained on the assumption that a considerable proportion of 

 the blacks are heterozygous. In the crosses of black and brown 

 we should naturally expect to get a larger percentage of browns 

 and lighter colors, and this we find. In the crosses of black with 

 light brown the proportion of browns and lighter colors is very 

 different from the Mendelian expectation in the light of the pre- 

 ceding results. If all the blacks were heterozygous, the blacks 

 should constitute 50 per cent, of the product instead of much 

 less than a third ; while, since some of the blacks may be safely 

 assumed to be homozygous, the black-haired offspring should 



Table III. 

 Showing the Inheritance of Hair Color of Parents from Grandparents. 



exceed 50 per cent. Crosses of browns with browns give a larger 

 number of browns than result from crosses of browns and light 

 browns ; but it is noteworthy that a considerable proportion of 

 black-haired individuals result from both these unions. 



While the data indicate that the inheritance of hair color in man 

 is, to a certain extent, alternative, it certainly does not justify us 

 in concluding that it is Mendelian. That it is to a certain extent 

 of the blended type is indicated by the fact that crosses of black 

 with light brown yield a much less proportion of blacks and a 

 greater proportion of browns than do crosses of blacks with brown. 

 If black were a typical Mendelian dominant it should occur in 



