HEREDITY 



337 



In the comparatively short period of time during which data on 

 human inheritance have been collected with an accuracy looking 

 toward testing the application of Mendelian principles, a considera- 

 ble mass of evidence has accumulated and many human traits have 

 been studied. Unfortunately, however, most of the records are in- 

 complete. This, together with the fact that many traits and charac- 



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Fig. 209. — Chart showing the inheritance of closely curled hair in a human family 

 through seven generations. Squares represent males; circles represent females. Solid 

 black indicates that the individual had the character; blank indicates the lack of the 

 character. Diamonds represent individuals concerning which nothing is known. 

 (After Gates: Heredity in Man, published by The Macmillan Company.) 



ters are not sharply defined and that many are undoubtedly the 

 result of more than one pair of allelomorphic genes, has thus far 

 rendered it impossible to as^^emble data necessary to anything like a 

 complete knowledge of human genetics. From a wealth of more or 

 less incomplete data we may select a single example that plainly 

 shows the inheritable character of a human feature, namely the 

 inheritance of close curly hair in a German family history extending 

 back to the sixteenth century. The data show the Mendelian dom- 



