THE PROBLEM OF INBREEDING 129 



determine the value of q by direct counting, as has 

 been done in the preceding simpler illustrations. 

 The calculation of the coefficients of inbreeding 

 may be greatly simplified in the case of long pedi- 

 grees by a system of counting which makes the 

 line of descent the unit rather than the individual. 

 This system is used in the above pedigree as an 

 illustration of method, although only 4 ancestral 

 generations are here considered. While each 

 individual animal which is eliminated because of 

 previous appearances in a lower ancestral genera- 

 tion is marked with an X, those at the apex of a 

 line of descent are marked with a cross within a 

 circle. These latter are all that need to be counted 

 directly. Thus the bull Sisera's Stoke Pogis 

 first appears in the second ancestral generation 

 as the sire of Davy Stoke Pogis. He next appears 

 (here marked with a cross within a circle) in the 

 same generation as the sire of Peg Weaver. He 

 will, by the general rule of coefficients of inbreed- 

 ing, not be counted as a "different" ancestor the 

 second time in this generation. But this auto- 

 matically eliminates his two parents in the third 

 ancestral generation, his four grandparents in the 

 fourth generation, and so on until in the twelfth 

 generation 1024 ancestors of Sisera's Stoke Pogis 

 will be so eliminated. The same consideration 

 applies in every other like case. 



Practically, then, the method of dealing with a 

 pedigree of this sort is first to go through and 



