Inheritance of Physical and Mental Traits 



273 



blondes never have brunette offspring, but brunettes may 

 have blondes. The extreme case is that of albinos with no 

 pigment in skin, hair, and iris. Two albinos have only albino 

 children, but albinos may come from two pigmented parents. 

 Similarly, straight-haired parents lack curliness, and 

 two such have only straight-haired children. Also two 

 tall parents have only tall children. Shortness is the trait: 

 tallness is a negative character. Also when both parents 

 lack stoutness (are slender), all children tend to lack it. 



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(N)i#[^^#i i50 ihoWiiO 



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Fig. So. — Inheritance of monilithrix — a positive cliaracter. Black symbols 

 represent affected individuals. — .Anderson. 



We may now consider briefly the inheritance of certain 

 pathological or abnormal states, to see in how far the fore- 

 going principles hold for them also. We shall find that 

 sometimes the abnormal condition is positive, due to a new 

 trait; but sometimes, on the contrary, the normal condi- 

 tion is the positive one and the trait is due to a defect. 



Among conditions due to a new determiner may be men- 

 tioned a beaded peculiarity in the form of the hair, called 

 monilithrix. Affected persons tend to ha\'e affected off- 

 spring (Fig. So). Two unaffected i)arents do not ordinarily 



