CHARACTERISTICS OF PEDIGREES — HOMOZYGOSIS 



57 



In this method of calculation, the percentage of homozygosis 

 under random mating is assumed to be 50 per cent. The average 

 percentage of homozygosis is equal to J (1 + /o) X 100, or on a 

 percentage scale of to 100 for the increase of homozygosis from 

 50 to complete homozygosis, 100 per cent, the value of 



/ = #(l)n + n' + l( 1+/a ) 



where S equals summation. 



It is possible to consider f as Wright does, a coefficient of inbreed- 

 ing. It is perhaps more properly the percentage increase of homo- 

 zygosis brought about by the system of breeding. To increase 

 homozygosis the ancestor must be common to both sire and dam. 

 The n and n' are the number of generations from sire and dam re- 

 spectively to the ancestor common to each. If the common an- 

 cestor is inbred, its coefficient of inbreeding f must be worked out 

 for his pedigree first. Otherwise the value of / is considered zero. 



The steps in the calculation of the pedigree of King Walker are 

 as follows: King Walker has as common grandsire Admiral Walker. 

 He also traces through the paternal grandsire and maternal grand- 

 dam to Lillian Walker. All common lines tracing back from the 

 sire to the common ancestor and thence forward to the dam and 

 passing through no individual more than once are thus included. 

 In tabular form we have f Q as given in the following protocol. 



INDIVIDUAL 



COMMON ANCESTORS OF 

 SIRE AND DAM 



fa 



n 



n' 

 1 



3 



(l ) n + n' +1(1+/a) 



King Walker 40358 



Admiral Walker 25755 

 Lillian Walker 38944 





 



1 



2 



0.1250 

 0.0156 









0.1406 



or the per cent of probable homozygosis J (1 + 0.1406) = 57.03. 



As another illustration, the pedigree of the Holstein-Friesian cow 

 Korndyke Butter Girl Johanna 2d, 183646 may be taken (see p.58). 



This pedigree displays a fairly large amount of inbreeding'. The 

 animals repeated first are Korndyke Butter Boy, Johanna 

 Aaggie 2d's Lad, Manor DeKol. The animals found in the pedigree 

 of the repeated animals are shown as the open circles containing the 

 cross. Korndyke Butter Boy is himself inbred so that it is neces- 



