CHAPTER 1 



2. Different genotypes in near-identical en- 



vironments: 

 Phenotypic difference — one small and one 



large bean from genetically different 



pure lines. 

 Phenotypic similarity — two medium sized 



beans from genetically different pure 



lines. 



3. Identical genotypes in different environ- 



ments: 



Phenotypic difference — one bean plant 

 grown in the light is green while another 

 grown in the dark is white, though both 

 are from the same pure line. 



Phenotypic similarity — if two rabbits 

 come from a certain pure line (geneti- 

 cally black rabbits), both will have black 

 coats even though one individual grew 

 at high and the other individual grew 

 at low temperatures. 



4. Different genotypes in different environ- 



ments: 

 Phenotypic difference — a rabbit from a 

 genetically black line, grown in a cold 



climate, has black fur, while a rabbit 

 from a Himalayan line, grown under 

 temperate conditions, is Himalayan, i.e., 

 white except for the extremities (paws, 

 tail, snout, and ears) which are black 

 (see Figure 1-2). 

 Phenotypic similarity — a rabbit from a 

 genetically black line grown at a mod- 

 erate temperature and a rabbit from 

 a genetically Himalayan line grown at a 

 cold temperature are both black furred. 

 The case of coat color in rabbits is instruc- 

 tive in another respect. The rabbit that is 

 genetically black will always produce a black 

 coat no matter what the temperature, so 

 long as it is not lethal. For this genotype 

 there seems to be no range of pheno- 

 typic expression with respect to temperature 

 variations. In the Himalayan strain, how- 

 ever, the situation is different, as already de- 

 scribed in part. If grown at very high tem- 

 peratures such rabbits would have coats that 

 are entirely white. In this case the pheno- 

 typic range of reaction, or norm of reaction. 



■^H 



FIGURE 1-2. Male Siamese cat, grown under temperate conditions, slwwing tlie 

 same pigmentation pattern as the Himalayan rabbit. {After C. E. Keeler and V. Cobb.) 



