Neo-Mendelism 



93 



On the other hand, facts have begun to appear which 

 seem contrary to this view. When the idea of Unkage 

 began to be developed the breeding expectations were 

 modified in accordance with it. For example, when it 

 is discovered that tall individuals always have smooth 

 seeds this fact is explained as Unkage. The inference is 

 that there never can appear a tall plant with wrinkled 



WT5 

 OO 



Tall Smooth Parent 



OO 



.'. F2 Shows 3 : I Ratio 

 (3 Tall Smooth : I Dwarl WiinkleJ) 



Dwari WHnkled 

 Parent 



Fig. 25. — Diagram showing how linkage would limit the possible 

 kinds of gametes. This mechanism will explain simply and accurately 

 the " coupling " and " antagonism " of the previous diagrams ; this mental 

 picture of chromosomes, suggested by Emerson and developed fully by 

 Morgan, is now generally accepted by geneticists. 



seeds or a dwarf plant with smooth seeds, for if there is 

 linkage and the chromosome is the indivisible unit ot 

 inheritance it would be impossible for tallness and 

 smoothness to become separated. 



This was the situation a few years ago, when suddenly 

 there appeared what corresponds to tall individuals 

 with wrinkled seeds and dwarf individuals with smooth 

 seeds. These unusual types appear rather rarely as a 

 general rule, although in a few special cases they have 

 appeared as frequently as 20 in 100. The work was done 

 with Drosophila (the fruit fly) under such conditions 



