E. L. Green, Ph.D., and D. P. Doolittle, Ph.D. 



SYSTEMS of MATING 



USED in MAMMALIAN GENETICSt 



Mammalian geneticists use a variety of mating systems, each designed to accomplish 

 a specific purpose. To use the systems effectively, it is necessary to know what each 

 system is, when it can be used, and what its theoretical genetic consequences are. 

 This paper describes seven systems of mating which have passed into general use by 

 mouse geneticists. Each system will be described by means of its mating types and 

 their probabilities through successive generations. In some cases reference will be 

 made to the kinds of genotypes and their probabilities, in particular to the probability 

 of heterozygotes. 



The theory of systems of matings has been extensively developed by Wright, 1442 

 Bartlett and Haldane, 56 and Fisher, 375 on whom we have drawn heavily for this 

 exposition. The system later called the " cross-backcross-intercross system" has not 

 been analyzed heretofore; its theoretic consequences are presented here for the first 

 time. We are indebted to Dr. George D. Snell who described the system to us and 

 who has been the first to use it. 



The following sections outline the analysis of the mating systems after first defining 

 some necessary symbols and describing the general steps of the analytical method. 

 The last section suggests a few practical rules for the breeders of laboratory animals 

 who desire to improve the genetic quality of mice, rats, rabbits, and other mammals 

 for research. 



| The authors gratefully acknowledge the support of the Sagamore Foundation and 

 the Richard Webber Jackson Memorial Fund. 



