THE PROBLEN OF INBREEDING 133 



first on one side of the pedigree (either the sire's 

 or the dam's) then on the other side. 



If only 1 and 2 are to be found in the pedigree, it 

 means that the sire and the dam are totally un- 

 related (within the limits covered by the pedigree 

 in the particular case). On the other hand, the 

 occurrence of 3 means that sire and dam are in 

 some degree related, and that a portion of the 

 observed inbreeding arises because of that fact. 

 Now the coeflScients of inbreeding, in and of 

 themselves, tell nothing about what proportionate 

 part has been played by these three elements in 

 reaching the final result. It is a matter of great 

 importance to have information on this point, 

 because of its genetic significance. It is now pro- 

 posed to describe a general method for obtaining 

 this desired information. 



The first step in the method, stated briefly, is to 

 break up the pedigree elimination table formed 

 to get the successive values of Pn+u in our for- 

 mer notation, into four different parts. One of 

 these parts will include the primary reappearance 

 on the sire's side of the pedigree of such animals 

 as appear first on the same side. This may be 

 called the "male only" table. The second part 

 will include the primary reappearance on the 

 dam's side of such animals as first appear on the 

 same side. This is the "female only" table. 

 The third part will include the primary reappear- 

 ance on the dam's side of such animals as first 



