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UNITED STATES DEPARTMENT OF AGRICULTURE 

 BULLETIN No. 1090 



Washington, D. C. 



PROFESSIONAL PAPER 



November 15, 1922 



THE EFFECTS OF INBREEDING AND 

 CROSSBREEDING ON GUINEA PIGS 



I. DECLINE IN VIGOR 

 II. DIFFERENTIATION AMONG INBRED FAMILIES 



By SEWALL WRIGHT 



Senior Animal Husbandman in Animal Genetics, Animal Husbandry 

 Division, Bureau of Animal Industry 



CONTENTS 



I. Decline in Vigor: 



Earlier Views on Inbreeding . . . 

 Plan of the Experiments .... 

 History of the Gainea-pig Stock 

 System of Mating, Care, and Feed . 



The Data Recorded 



The Characters Studied .... 

 Indexes for Growth and Mortality . 

 Changes in Inbred and Control Stocks 



Sex Ratio 



Tests for Disease Resistance . . . 

 Summary 



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3 



3 



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9 



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18 



20 



29 



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31 



I. .Decline in Vigor— Continued. Page 

 Appendix— Tables 6 to 22 32 



II. Differentiation Among Inbred Fam- 



ilies: 



Differentiation in Color 37 



Abnormalities 38 



Differentiation in Vigor 42 



Detailed Study of Family Characters . 45 

 Reicords of Five Families in Recent 



Years .55 



Summary 57 



Appendix — Tables 7 to 15 59 



WASHINGTON 

 GOVERNMENT PRINTING OFFICE 



1922 



