578 THE PROBLEMS OF HEREDITY AND THEIR SOLUTION. 



owing" to the masking effects of conditions, etc., have great difficult}" 

 in distinguisliing the tliree forms in the second generation. There 

 would, besides, be twice as many heteroz^^gous individuals as honio- 

 z3"gous individuals of each kind, giving a symmetrical distriljution of 

 heights, and who inig-lit not — in pre-Mendelian days — have accepted 

 such evidence, made still less clear by influence of conditions, as 

 proof of continuous variation both of zygotes and gametes ( 



Suppose, then, that instead of two pure types, we had six or eight 

 Ijreeding tog-ether, each pair forming their own heterozygote, there 

 would be a very remote chance of such purity or fixity of type, whether 

 of gamete or z3^gote, being detected. 



Dominance, as we have seen, is merely a phenomenon incidental to 

 specific cases, between which no other common property has 3^et 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 evidentl}' no universal dominance. From 

 the tables of Basset hound pedigrees there is clearly no detinite domi- 

 nance of either of the coat colors. In the case of eye color the pub- 

 lished 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 3"et untouched. It may i)erfectl3^ well be 

 that we shall be compelled to recognize that in many cases there is no 

 such purit3% and that the characters ma3" be carried 1)3' the gametes in 

 an}^ proportion from zero to totalit3", just as some substances ma3' be 

 carried in a solution in any proportion from zero to saturation without 

 discontinuous change of properties. That this ma3" be found true in 

 some cases is, on any hypothesis, certain; but to prove the fact for an3" 

 given case will he an exceedingly difficult operation, and I scarcely 

 think it has been yet carried through in such a wa3" as to leave no 

 room for doul)t. 



Conversely, the absolute and universal purity of the gametes has 

 certainly not 3'et been determined for an}" case; not even in those cases 

 where it looks most likel}" that such universal purit3' exists. lm])air- 

 ment of such })ui-ity we mav conceive either to occur in th(^ form of 

 mosaic gametes, or of gametes with l)lended properties. On analogv 

 and from direct evidence we haA'c ever3" right to believe that gametes 

 of both these classes ma}" occur in rare and exceptional cases, of as 

 3"et unexplored nature,^' but such a phenomenon will not diminish the 

 significance of observed purity. 



" It will be iiiKk'rstood from what follow.s that the i-xistence of mosaic zygotes is no 

 proof that eitlier c(Miii)()nent gamete was mosaic. 



