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Comments 



Robinson: I question here, and in Doctor MacKey's presentation, the 

 assumption of the superiority of the heterozygote, i.e., the importance 

 of overdominance, particularly in quantitative characters. Reference has 

 been made to work in Drosophila for the importance of epistasis. I 

 cite the work of Vethukiv (Evol., 1954) and by Vethukiv and Beardmore 

 (Genetics, 1959) where the later results do not support the conclusion 

 of important epistasis given in 1954. 



The importance of super- or overdominance in quantitative char- 

 acters has, to my knowledge, still to be convincingly demonstrated. 



Heterosis occurs in variety crosses of maize, but neither overdomin- 

 ance nor epistasis may be necessary for an adequate explanation of the 

 heterosis. Genetic diversity resulting from different alleles in different 

 parents could account for the heterosis observed. 



Caldecott: I would make three points because I believe they reflect 



