THE PROBLEM OF INBREEDING 119 



and by the same process, 



z _ 100 (8-4) _ 

 8 



Z3 = 100(16-5) = 6873) 

 16 



Z4 = 100J32-6) = 8125) 



and so forth. 



The values of the successive coefficients for 

 parent X offspring for 16 ancestral generations are 

 given in Table 2. 



By comparison of this table with Table 1 it is 

 evident that while the increase in intensity of 

 inbreeding is not so rapid in the first few ancestral 

 generations by this parent X offspring type of 

 breeding as with the brother X sister type, by the 

 time the tenth ancestral generation is reached the 

 values are for practical purposes the same. 



The curve of inbreeding for continued parent 

 X offspring breeding is shown in Fig. 1. 



ILLUSTRATION III. FIRST-COUSIN X FIRST-COUSIN 



BREEDING 



As a third illustration may be taken the case of 

 continued cousin mating. Such breeding repre- 

 sents the next step in decreasing intensity of 

 inbreeding beyond the parent X offspring type. 



