84 THE MENDEL JOURNAL 



fingers of the hand are apparently, like the thumb, 

 made up of two joints, instead of three as in the normal 

 hand. It is the middle one of the three joints which 

 has to all appearance disappeared. There is some 

 reason to believe that it has not actually disappeared, 

 but that it is vestigal in size and has become fused on 

 to the last joint. However, for practical purposes 

 we may speak of the peculiarity as a two-jointed 

 condition of the fingers. 



The history of the family in which this peculiar 

 condition is present is known for seven generations. 

 The first three generations are incomplete, but 

 the remaining four are complete and comprise a 

 fairly numerous collection of individuals. The whole 

 seven generations include one hundred and seventy- 

 four persons. We may divide the marriages into 

 two classes, i.e., those in which an abnormal person 

 married a normal one, and those in which an extracted 

 normal individual derived from this family married 

 a normal one from outside of it. The first type of 

 marriage will be represented as D R x R R, and the 

 latter type by R R x R R. The brachydactylous 

 condition is shown by the observations on this 

 family to be a dominant one. Now, what is the 

 Mendelian expectation as to the offspring from these 

 two types of marriage ? In the first type two classes 

 of individuals, i.e., short-fingered and normal-fingered, 

 are expected in the offspring. And it is further 

 expected that these two classes will be present in 

 approximately equal numbers. Once more an appeal 

 to the facts of human pedigrees confirms Mendelian 



