XV 



MAN 



173 



occur, the numbers of 

 the two classes are, on 

 the average, equal. 

 (The sum of such 

 families in the com- 

 plete pedigree is 

 thirty-nine affected 

 and thirty-six nor- 

 mals.) It is obvious 

 that these are the 

 conditions which are 

 fulfilled in a simple 

 Mendelian case, and 

 there is nothing in this 

 pedigree to contradict 

 the assertion that 

 brachydactyly, what- 

 ever it may be due to, 

 behaves as a simple 

 dominant to the nor- 

 mal form, i.e. that it ^ 



depends upon a factor 

 which the normal does 

 not contain. The re- 

 cessive normals can- 

 not transmit the 

 affected condition 

 whatever their an- 



