ON INBREEDING IN JERSEY CATTLE. 649 



INBREEDING IN JERSEY CATTLE. 



THE POSSIBILITY OF YIELD AND QUALITY OF MILK BEING 

 INHERITED IN A SEX LINKED MANNER. 



BY 



A. D. BUCHANAN SMITH, 

 Animal Breeding Besearch Department, The University, Edinburgh. 



For some time past the methods employed by breeders in the construction of 

 various breeds of commercial livestock have been studied in this department. The 

 analysis of the various breeds has been made by means of Wright's coefficient of 

 inbreeding, which in essence is based on Galton's Law of Ancestral Inheritance, with 

 this important addition, that inbreeding cannot be considered to have full genetic 

 effect on the homozygosity of the animal unless the ancestor to which the animal is 

 inbred appears in the pedigrees of both the sire and dam of that animal. Figure I 

 gives examples of Wright's coefficient. The two lower pedigrees show that, although 

 in both of them the common ancestor, x, is a grandsire and a great grandsire, inbreeding 

 only occurs in the left-hand pedigree since, on the right-hand one, x does not appear 

 as an ancestor of the dam of the individual. 



[Wright's}. 



'D 



r 



A- 



'c- 



X 



E 



X 



Sire to daughter coefficient 25. Half-sister to Half-brother 



coefficient 12.{>. 



J 



X ,\ 



^- A i 



,F F 



C^ ^ . 'c' 



I Common Grandsire and , 



*G Great Grandsire. 'g 



Coefficient 6.25. Coefficient nil. 



The common ancestor appears on 

 only the sire's side of the pedigree. 



Wright's Coefficient F = (i)'*+"'+ V+fa) 

 n and n' represents the number of generations which the common ancestor is 

 distant from the sire and dam respectively. Fa is the coefficient of inbreeding of the 

 common ancestor. 



