222 LIFE: ITS NATURE AND ORIGIN 



One good feature of these older clinical aspects is that they 

 stressed the fact that patients differ widely in potentialities, and 

 that it is not alone a stereotyped "disease" which must be treated, 

 but also the variable reactions of patients having the disease, or 

 exposed to conditions which produce it. These mainly genetic 

 differences in individuals in colonies of animals kept for experi- 

 mental purposes, and even in litter mates, were discussed at a 

 Conference on Animal Colony Maintenance, 5 and constitute a 

 criterion in judging the results reported on animal experiments. 

 In his introductory remarks Dr. Edmond J. Farris (Wistar Insti- 

 tute) stated that in his undergraduate days "type" experiments in 

 mammalian physiology "hardly ever agreed with the textbook 

 picture. This was common classroom experience." 



Dr. F. B. Hutt of Cornell University points out that the physi- 

 ologist, the pathologist, and particularly the nutritionist want a 

 steady supply of animals showing minimum variability. "The 

 geneticist, on the other hand, thrives on variability. It is his stock 

 in trade. The recalcitrant rat that lingers on long after its or- 

 thodox litter-mates have terminated their abbreviated careers on 

 the diet lacking vitamin Q is merely a statistical nuisance to the 

 nutritionist, but to the geneticist it is the potential progenitor of 

 a race able to manage nicely with much less vitamin Q than mil- 

 lions of other rats that are less fortunate in the matter of genes . . . 

 Because some biologists still think that genes cause only such 

 'sports' as freaks of hair color, of hair form, of eye-color, or other 

 inconsequential mutations, but have little or no effect on funda- 

 mental physiology, these examples are chosen to refute that view." 



In yellow mice the gene A y (one of a series of allels affecting hair 

 color in the common house mouse) is lethal to the homozygote, which 

 dies in utero. The mice born alive show a ratio of 1 non-yellow to 

 2 yellow heterozygotes, which latter are characterized by (1) adiposity; 

 (2) a subnormal metabolism; (3) slightly greater body size, apart from 

 their excessive fat; (4) lower susceptibility to spontaneous mammary 

 carcinoma than their black or brown litter mates. 6 In fowl a dominant 

 autosomal gene produces the condition "frizzle," the feather curling 

 back toward the head. When "frizzles" are mated, the progeny show 

 three types: so extremely frizzled as to appear woolly; standard frizzled 

 type; not frizzled. The ratio is 1:2:1. The extremely frizzled birds 

 become more or less bare as their feathers break off; and these 

 homozygous birds differ from normal fowl in (l)viability; (2) rate 

 of growth; (3) age of sex maturity; (4) metabolism; (5) rate of heart 



