480 Orgamsim Are Froducts of Heredity and Enviroiwient unit ix 



White — eye 



Wingless 



Fig. 429 The fruit fiy on. the right is normal. The others show four inheritable 

 changes that have occurred. What are they? What do the words strap and miniature 

 refer to? What other wing character have you read about? 



Of course, when the new gene is reces- 

 sive there is no outward sign of the 

 change until a later generation, when 

 two such new genes may come together. 

 Try to illustrate how this works out by 

 doing Exercises i and 2, 



Changes in genes may produce harmful 

 effects in the organism. A^Iost mutations 

 do. Short (vestigial) wings are clearly 

 harmful to the fruit fly; most of the other 

 mutations shorten the life of the fly. By 

 far the greater number of mutations are 

 so harmful that the organism dies; others 

 merely weaken the animal or plant; a few 

 are an advantage to the organism. 



Alutations have been discovered in 



many organisms — corn, chickens, rabbits, 



„ ^ , . , , , , , mice, man, and many others. Any organ- 



l-iG. 430 Mutant (lert) in barley produced by . u u u ' r ' 



x-ray treatment. How does it differ from the ^^^ ^^^^ ^'^O^^'S ^^^ result of a mutation 



nor7nal plant at the right? (stadler) is called a TTfUtant, 



