32 The Problems 



If however instead of pure extreme varieties we were to 

 take a pair of varieties differing normally by only a foot or 

 two, we might, owing to the masking effects of conditions, 

 &c., have great difficulty in distinguishing the three forms 

 in the second generation. There would besides be twice as 

 many heterozygous individuals as homozygous individuals 

 of each kind, giving a symmetrical distribution of heights, 

 and who might not in pre-Mendelian days have accepted 

 such evidence made still less clear by influence of con- 

 ditions as proof of Continuous Variation both of zygotes 

 and gametes ? 



Suppose, then, that instead of two pure types, we had 

 six or eight breeding together, each pair forming their own 

 heterozygote, there would be a very remote chance of such 

 purity or frxity of type whether of gamete or zygote being 

 detected. 



Dominance, as we have seen, is merely a phenomenon 

 incidental to specific cases, between which no other common 

 property has yet been perceived. In the phenomena of 

 blended inheritance we clearly have no dominance. In the 

 cases of alternative inheritance studied by Galton and 

 Pearson there is evidently no universal dominance. From 

 the tables of Basset hound pedigrees there is clearly no 

 definite dominance of either of the coat-colours. In the case 

 of eye-colour the published tables do not, so far as I have 

 discovered, furnish the material for a decision, though it is 

 scarcely possible the phenomenon, even if only occasional, 

 could have been overlooked. We must take it, then, there 

 is no sensible dominance in these cases ; but whether there 

 is or is not sensible gametic purity is an altogether different 

 question, which, so far as I can judge, is as yet untouched. 

 It may perfectly well be that we shall be compelled to 

 recognize that in many cases there is no such purity, and 



