UNITED STATES DEPARTMENT OF AGRICULTURE 

 BULLETIN No. 1121 



Washington, D. C. 



PROFESSIONAL PAPER 



December, 1^22 



THE EFFECTS OF INBREEDING AND 

 CROSSBREEDING ON GUINEA PIGS 



m. CROSSES BETWEEN fflGHLY INBRED FAMILIES 



By SEWALL WRIGHT 



Senior Animal Husbandman in Animal Genetics 

 Animal Husbandry Division, Bureau of Animal Industry 



CONTENTS 



Page 



Introduction 1 



The Inbred Families 2 



Crossbreeding Experiments 2 



Description of Tables 3 



Allowance for Seasonal Fluctuations ... 5 



Allowance for Heredity 10 



Allowance for Age of Dam 12 



Allowance for Sex 12 



Significance of Differences 13 



Results 15 



The Percentage Born Alive 16 



The Percentage Raised Among the Toung 



Born Alive 18 



The Percentage Raised of All Young Born . 20 



Birth Weight 21 



Daily Gains 22 



Weight at Weaning 23 



Page 



Adult Weight 24 



Frequency of Litters 26 



Age of Maturity 27 



Complete Sterility 28 



Size of Litter 28 



Total Fertility 30 



Coat Color 32 



Resistance to Tuberculosis 32 



Early Views on Inbreeding 33 



Pre-Mendelian Experiments 34 



Mendelian Heredity and the Problem of 



Inbreeding 35 



Mathematical Considerations 39 



Comparison of Results with Theory ... 46 



Summary and General Conclusions ... 48 



Llteratnr* Cit«d 09 



WASQINGTON 



GOVERNMENT FEINTING OFFICE 



1922 



