io8 



Eye-Colours 



[CH. 



too vague he instituted a more critical classification, which 

 led to the discovery that the presence of brown pigment on 

 the anterior surface of the iris behaves as a dominant to the 

 absence of such pigment, which is a recessive character. 



Parents without the pigment in question have exclusively 

 children who are similarly without it, whereas persons 

 possessing the brown pigment may be either homozygous 

 or heterozygous in that respect, and their offspring follow 

 the numerical rules with fair exactitude. 



0"x 



9 



0"0" 0" 9 0" O" Q 



o" o* o" o* 9 o" 



9 



9 



<y 



& 



O" 



9 



9999999 



i 



Dorrviruuvba 



^ Dupl&x. Self- colour 1 



O-^^/'^r; 



O Simplex. 



Fig. 1 8. Two pedigrees showing the descent of eye-colour (after Hurst). 



"Brown" eyes are no doubt all dominants, and "blue" 

 eyes are very often recessives; but, on the other hand, many 

 eyes which would be called "light" have some of the 



