COLOR INHERITANCE IN MAMMALS 



XI, Man — Mode of Inheritance of Unusual Family Traits Easy to Analyze. 



Situation More Obscure in Case of Common Variations. Variations in 



Hair, Skin, and Eye Color Must be Considered Together. At Least 



Two Distinct Kinds of Dilution of Color Probably Exist, 



Which Are Combined in the Blond Nordic Race 



lai 



la2 

 las 

 lb 



W, w W — Premature grayness of 



certain families. 

 V, V V — white spotting. 



C, 



2a, 

 2a 2 

 2a 3 



c — albini.sm in many cases. 



Variations of this class, 

 common in white race, 

 reduce dark eyes to 

 light, red hair to flaxen, 

 but have little effect on 

 black hair. Reduction 

 of skin color. 



Variations of this class, 

 common in white race, 

 reduce dark eyes to 

 light or even albinotic, 

 black hair to red, yellow, 

 flaxen, or white, de- 

 pending on factors of 

 class lb. Auburn and 

 brown intermediate 

 variations. Reduction 

 of skin color. 



2b 



A M()XG Ininian beings, the common 

 / \ variations in hair, skin, and eve 

 L \. color resemble many of those of 

 the lower mammals. In spite of 

 this similarity, however, the mode of 

 inheritance is. in most cases, still very 

 obscure. It is only in the case of cer- 

 tain rare variations which are obviously 

 associated with particitlar families that 

 unit factors can be said to be conclu- 

 sively demonstrated. 



pre:*iature grayness 



A typical example of such a varia- 

 tion is present in a pedigree ( MM ) 

 given by Pearson. Nettleship, and 

 Usher. ^ Among the affected persons 

 of this family, the hair became gray in 

 youth. In each case, one parent was 

 prematurely gray, while the normal 



children showed no tendency to trans- 

 mit the trait. In the published pedi- 

 gree, the trait has been handed on for 

 at least hve generations without a break. 

 I'robably it went nuich farther back 

 as the authors give a translation of an 

 old Gaelic curse said to have been pro- 

 nounced in the fourteenth century. 



"In the time of most numbers shall 

 weakness come o'er them. 



In the time of most weakness, shall 

 strength then restore them. 



In their prime in their youth like the 

 rushes they'll grow. 



As withers the bracken be their man- 

 hood laid low. 



O'er the child's clustering ringlets shall 

 age spread its snow." 



^^'e have here clearly a dominant 

 hereditary unit which is passed on in- 

 dertnitelv without attrition in spite of 

 union with fresh normal stock in each 

 generation. As regards its relationshi]) 

 to color factors in the lower mammals. 

 it seems closest to those which have 

 been put in class laj. There is a gen- 

 eral inhibition of hair pigment regard- 

 less of quality. The dominant factor 

 for grayness in horses has the further 

 similarity in that the whiteness in- 

 creases with age. 



Holmes and Schofield- have recently 

 published a pedigree in which a small 

 white lock was present only in males, 

 but could be transmitted by the mother. 

 The inheritance was not sex-linked, as 

 affected males could transmit it to their 

 sons. The authors attribute it to sex- 

 limited inheritance. According to this 

 view, the trait is inherited as a domi- 

 nant imit bv the usual mechanism, but 



'Pearson, K., E. Xettlesliip. and C. H. LMier, 1913, ".A ^Monograph on Albinism in Man.' 

 Dulau and Co.. London. 



■^Holmes, .'^. J., and R. O. Scliofiek!. Jour. Her.. 1917. 8:.559-o62. 



227 



