Chapter 3 

 GENES AND CHARACTERS 



Genes act at various stages during the development of the 

 organism to produce definite characters but, although each gene 

 acts always in cooperation with other genes and with the environ- 

 ment, the effect of the environment may not be the same upon all 

 genes. Some genes behave so differently in different environments 

 that the characters they produce are strikingly different; other 

 genes appear to produce the same result under all known environ- 

 mental conditions. It cannot be too strongly emphasized that 

 heredity and environment are factors which are continually 

 interacting. The developed character is the product of a certain 

 hereditary constitution and a certain set of environmental con- 

 ditions both of which are acting during development to produce 

 the character in question. 



Environmental Effects 



As an illustration of characters which develop in the same 

 way under different environmental conditions and of those which 

 are different if the environment is different, some of the genes 

 that affect the color of the fruits in maize may be cited. Certain 

 strains always have white ears because they have genes that 

 produce white fruits under apparently all conditions of the en- 

 vironment. Other strains have genes that produce red fruits 

 even when the plant develops under a variety of conditions, and 

 such strains always have red-fruited ears. In some strains, how- 

 ever, there is a gene that produces different results, depending 

 upon whether the ear is kept dark or is exposed to the light as it 

 develops (Fig. 9). If the ears of plants that have this "sun-red" 

 gene are allowed to mature normally in their husks w^here they 

 are completely protected from sunlight, the mature ears are 

 white. On the other hand, if the husks are removed from the 

 developing ear, the ear turns a bright red. If only portions of 

 the ear are exposed, only those portions will become red; the 



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