34 HEREDITY OF SKIN COLOR IN NEGRO-WHITE CROSSES. 



Table 30. — Distribution of eye color in offspring of parents with given amount of iris 

 pigmentation. — Continued. 



<L) DARK BROWN X BROWN. 



(M) DARK BROWN X DARK BROWN. 



(N) BLACK X DARK BROWN. 



. la.. 

 . 18.. 



dk. br. 



dk. br. 

 dk. br. 



Since our matings did not include two pure blue-eyed parents, 

 the simplest case of heredity (the mating of two negatives) can not 

 be tested here. Hazel we have regarded as usually a simplex (hetero- 

 zygous) condition, and on this hypothesis two hazel parents should 

 produce blue-eyed, bro\vn-eyed, and hazel-eyed offspring again; but 

 until we Icnow how many factors are involved in bro\\-n iris color we can 

 not say in what percentage of cases blue should reappear. Actually, in 

 section (.4), in 9 offspring there is i case of dark brown iris; none of 

 blue, and 5 of hazel again. But in sections (£) and (7), when hazel 

 is used as one parent, a few blues appear in the offspring; actually 

 6 in 87. On the hypothesis of two factors for black in eye color we 

 might expect i child in 4, in these two matings, to be blue-eyed. On 

 the hypothesis of four factors for black in eye color we should look for 

 I blue-eyed child in 16. The actual result favors the hypothesis of four 

 factors for black in iris pigmentation of negroes. Brown X brown gives 



