GENIC ACTION IN THE MOUSE 229 



against a genetically homogeneous background. Histocompatibility is essential for 

 transplantation. Quantitative evaluation of effects of particular genie substitutions 

 depends upon uniformity of the base line used for comparison. Uniformity of genetic 

 background may come about in three different ways. 483 With the increasingly wide- 

 spread use of inbred strains, many of the stocks in which deviants are detected may be 

 inbred, so that from its first appearance a new mutant may be segregating against an 

 inbred background. The best way to maintain high congenicity is by repeated back- 

 cross of the mutant heterozygote to the strain of origin. If a new mutation is found in 

 a genetically heterogenous stock of animals, a new inbred strain may be produced by 

 successive brother-sister matings with forced heterozygosis for the mutant allele, or the 

 mutant allele may be placed on an existing inbred background by many repeated 

 backcross generations. It may be worth mentioning that there are at present in the 

 Jackson Laboratory alone 67 stocks designed to place and maintain specified mutant 

 genes on inbred backgrounds. 751 Twenty-five of these mutants are maintained con- 

 genic with C57BL/6J, which makes for excellent uniformity between experiments and 

 provides very favorable material for new genotypic combinations and comparisons, 

 and for double-genic substitutions in transplantation experiments. There is evidence, 

 however, that this one inbred strain is not the ideal background for all mutant genes. 

 As a final plea in methodology of mammalian physiologic genetics, I would like 

 to encourage very widespread use of controlled genetic material by investigators in 

 other biomedical disciplines. The analyses of genie action cited in this paper include 

 many excellent examples of such utilization. Physiologic geneticists are forced, by 

 the diversity of the paths of genie action which they encounter, to be jacks of many 

 trades and face the very real possibility of being masters of none. The studies of W- 

 series anemias have involved active participation by pathologists, biochemists, embryo- 

 logists, and physiologists. Multidisciplinary approach to analysis of the action of a 

 single set of genes has been very useful in this case. Similar collaboration between 

 geneticists and other types of investigators may prove profitable for many other studies. 



DISCUSSION 



Dr. Burdette: Thank you, Dr. Russell. Dr. Russell's paper will first be discussed 

 by Dr. D. L. Coleman. 



Dr. Coleman : I would like first to commend Dr. Russell on her stimulating and 

 comprehensive discussion of genie action in the house mouse. I would like to comment 

 further on two points to which she has alluded in her talk. First, I would like to clear 

 up a possible misunderstanding. I do not think that the tyrosinase picture is quite 

 as clear-cut as she has indicated. However, the best evidence at this time does suggest 

 the situation which she has described. 



The other point I would like to discuss relates to my particular studies on the dilute 

 mouse 214 and attempts to demonstrate how some of the methods which she has described 



