416 



G. F. SPRAGUE 



In the original paper by Comstock et al. (1949) a comparison is presented 

 of improvement limits of three definite breeding procedures. These were (1) 

 selection based on general combining ability using at least two single crosses 

 as testers, (2) recurrent selection for specific combining ability as proposed 

 by Hull (1945), and (3) reciprocal recurrent selections. The assumptions on 



75 



60 



ORIGINAL POPULATION 



62.5 675 72.5 775 82.5 87 5 92.5 97.5 102.5 



YIELD IN BUSHELS PER ACRE 



75 



60 



45 



30 



15 



IOWA 13 



QL — 



FIRST CYCLE 



625 675 72.5 77.5 825 87.5 



YIELD IN BUSHELS PER ACRE 



92.5 



97.5 



Fig. 26.5 — A comparison of the frequency distributions for yield in bushels per acre for top 

 crosses from the original Stiff Stalk Synthetic and after one cycle of recurrent selection. 



which these comparisons were based were stated by Comstock et al. and 

 will not be repeated here. The conclusions reached are briefly as follows: 



1. When dominance is incomplete methods 1 and 3 are essentially equal 

 and superior to method 2. 



2. If over-dominance is of major importance methods 2 and 3 will be 

 essentially the same and superior to method 1. 



3. When dominance is complete all three methods would be rather 

 similar. 



Thus method 3, reciprocal recurrent selection, would appear to be the 



