Linkage 



99 



a monohybrid ratio, the tall individuals always being 

 fed flowered, and the dwarf individuals always white 

 flowered. The results obviously arise from the fact 

 that T and R are linked, being located on the same chro- 

 mosome, as are also / and r. 



These linkage results, taken by themselves, might 

 seem to recommend the following interpretation. It is 

 really the chromosome itself that is the important and 

 indivisible unit in inheritance, while the distinction 



"LINKAGE" 



Dwarf White Parent 



Only 2 Gametes 



Possible 

 .'. F2 Shows 3 : i Ratio 



Fig. 17. — Diagram showing "dihybrid" behavior when genes are 

 linked. Fi produces only two types of gametes. 



between the various genes on a single chromosome is 

 purely arbitrary and unnecessary. In other words, why 

 need we assume that T and R are distinct genes, when we 

 would be equally justified in assuming that tallness and 

 redness are merely two of the effects })roduced by the 

 same chromosome ? This latter assumption may appear 

 attractive, but it becomes clearly im])ossil)lc when some 

 of the further breeding results arc considered. 



Following out the foregoing example (merely as an 

 illustration), when it was discovered that tall individuals 

 always had red flowers, this fact was explained as linkage. 



