174 GENETICS 



is the same as the number of pairs of chromosomes. The 

 numbers of groups and of pairs in certain organisms are as 

 follows : 



Drosophila melanogaster 4, Drosophila virilis 6, Garden 

 Pea 8, Sweet Pea 8, Maize 10. 



In man there are twenty-four pairs of chromosomes, in- 

 cluding the X's. It is to be expected therefore that there will 

 be found 24 groups of linked characters, one group sex- 

 linked, the other 23 groups typical Mendelian, in their 

 inheritance. But it will be a very long time before these 24 

 groups are identified. 



What Kinds of Characteristics are Found in the Different 



Linked Groups? Functions of the Different Chromosomes 



in Their Relations to Characteristics 



Have the different chromosomes different functions? Can 

 we classify their functions in any simple or systematic way? 

 Do certain chromosomes influence certain particular parts 

 of the body, or certain particular functions, while others 

 influence other parts or functions? 



Such questions can be answered by an examination of the 

 kinds of characteristics found in each of the linked groups; 

 this will show what kinds of characteristics are influenced 

 by each of the chromosomes. We give therefore the follow- 

 ing lists of a number of typical characteristics connected 

 with each chromosome in the fruit-fly. The characteristics 

 listed are all modifications of the normal characteristics 

 found in the typical wild fly. Hence for every characteristic 

 here listed there exists also a corresponding unmodified 

 normal characteristic. Each of the characters listed is the 

 result of modification of a single gene. 



