R. E. COMSTOCK 



and 



H. F. ROBINSON 



Norih Carolina Sfaie College 



Chapter 30 



Estimation of Average 

 Dominance of Genes 



This discussion will center around three experimental procedures used at the 

 North Carolina Experiment Station for investigating the degree of dominance 

 involved in the action of genes that affect quantitative characters of economic 

 plants. The objective is twofold: (1) to outline and, in so far as possible, eval- 

 uate these methods; and (2) by example, to point up the role of statistics in 

 genetical research. 



Basic criteria for the usefulness of a projected experiment are: (1) Will 

 data obtained provide a logical basis for inference relative to the research 

 objective? (2) Will the random variability in the experiment be of an order 

 that will permit satisfactory certainty of conclusions? The latter has obvious 

 statistical overtones, but statistics is not always deeply involved in the 

 former. In genetic work, random variability in the experimental material is 

 generated in part by the genetic mechanism, and can therefore be used as 

 a basis for inference in genetic problems. Hence statistics plays an inescap- 

 able role in both aspects of the evaluation of many genetic experiments. 



Examination of any proposed basis for inference must obviously center on 

 the premises involved and the validity of deductions predicated on those 

 premises. We will turn first, therefore, to description of the experiments and 

 the logical basis for the estimates they are designed to provide. 



THE EXPERIMENTAL DESIGNS 



The designs of each of these experiments have two aspects: (1) the genetic 

 background and (2) the field arrangement of the material on which data are 

 collected. 



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