652 



ON INBREEDING IN JERSEY CATTLE. 



The -writer is indebted to Dr. H. Comer, of Brook House, Southgate, London, 

 for the direction of his attention to this. Dr. Comer was breeding his herd of Jerseys 

 along these lines with notable results when unfortunately, owing to an outbreak of 

 foot and mouth disease, the herd had to be destroyed. Miss Robertson (1921) 

 contributed a paper to the Journal of Genetics from statistics of a herd of Kerry cattle 

 which had been recorded daily since 1904. The figures and suggestions in her paper 

 may perhaps be accommodated by this suggestion. The practice adopted in this 

 herd, when fresh blood is deemed necessary, is to introduce it by way of the female line. 



Figure III shows the line of transmission of a character inherited in a sex linked 

 manner. The sex linked factors are marked by a thick line. Where the contribution 

 is through the dam it is designated by a dotted line, for she may be heterozygous for 

 the sex linked character, and therefore the contribution in a population should average 

 at rather over half of that marked by the thick line through the sire. 



FlOUEE III. 



Inheritance, of a Sex Linked Factor in Cattle. 

 Pi P> Ps 



P4 



(J 



9 

 (J 

 9 

 <J 



9 



Alternatively the line of sex linked inheritance might perhaps be better understood 

 by the following diagram. 



Figure IV. 



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P, 



t 



XX 

 /XO 



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XX 



