Linkage 97 



results. Conversely, the occurrence of a certain type of 

 breeding result would serve as a clear indication that 

 more than one gene may be carried on a single chromo- 

 some, and thus as a further confirmation of the belief 

 that the chromosomes are the bearers of hereditary 

 characters. 



In 191 1, results of just this sort were obtained in 

 corn by Emerson (2), who stated: ''This is an example 

 of a feature w^hich is probably very widespread in the 

 plant world, but of which at present we know little." 

 Long before any further important work was done along 

 this line among plants, however, Morgan (5) published 

 the results of his very careful and intensive breeding 

 experiments with the fruit fly. His ideas have had a 

 profound influence upon subsequent work in genetics. 

 He has given us a more accurate picture of the hereditary 

 mechanism and one that fits the facts bettei than any 

 previously proposed. In simplest terms the picture is 

 this. Each chromosome is a rodlike structure, and 

 numerous genes are arranged in a line along this rod. 

 Thus Morgan further analyzes the germ plasm by accu- 

 rately locating the genes. (He does not attempt any 

 description in physico-chemical terms of the genes them- 

 selves or of the exact relation they may hold to the 

 chromosomes on which they are carried.) 



We cannot discuss here the many ways in which this 

 fundamental conception has cast light upon work in 

 genetics. Suffice it to say that it has resulted in a new 

 ''school" of geneticists whose experiments have been 

 more intensive, more exact, and in s(^mc ways more 

 "fundamental" than those of any previous school. To 

 date most of the linkage work has been done with the 



