INHERITANCE IN MANKIND 41 



Here the second pair in generation I. probably consist 

 of a pure - bred dominant brown and a pure - bred 

 recessive grey. Their offspring are all of the type 

 DR, and, when mated with recessives, produce together 

 eight brown-eyed children and six with grey eyes — 

 a good approach to the Mendelian equality. Other 

 similar pedigrees might be given, or may be traced. 

 In all cases care must be taken to consider a sufficient 

 number of individuals before drawing general con- 

 clusions about the problems of inheritance. 



Many diseases and malformations seem to depend 

 on a definite pathological condition, and to descend as 

 Mendelian dominants. The affection known as brachy- 

 dactyly, in which the fingers are shortened and possess 

 only one joint instead of two, is a dominant character, 

 the normal condition of the fingers being recessive. 



Two pedigrees of brachydactylous families have been 

 described. One, published by Farabee, is illustrated 

 below. In each case the affected parents married 

 normal persons, and, to simplify the diagram, the 

 marriages are not indicated. Moreover, the children 

 of unaffected parents were none of them affected, so, to 

 save space, they, too, are omitted from the figure. As 

 before, the signs to look for are the transmission of the 

 character through those alone who possess it, and the 

 equality in number of the affected and non- affected 

 among the children of affected and normal parents. 



The following table gives the results of Farabee's 

 inquiries : — 



