294 The Genetics of the Dutch Rabbit — A Reply 



and I are agreed in supposing that the "residual heredity," when 

 analyzed, will probably be found to be factorial. He refuses to con- 

 sider any other possibility; I have preferred to use a non-committal 

 term, until a fuller experimental analysis has been made. 



The chief difference between Punnett's views and mine lies in the 

 number of factors assumed to be in operation in the various crosses and 

 the relative importance of these factors. I have assumed that one 

 Dutch factor was present in each race and that the slight genetic 

 variation seen in each uncrossed race, and also the modifications 

 resulting from crossing, were due to minor or modifying factors 

 (collectively "residual heredity"). Punnett ignores genetic variation 

 in uncrossed types and the possibility of modification through minor 

 genetic factors. He assumes that three independent major factors are 

 concerned in the production of Dutch patterns. I have assumed the 

 existence of three allelomorphic conditions of one and the same factor 

 (one in each race), whereas Punnett assumes the existence of three 

 independent factors which in different combinations produce the three 

 races. It should not be difficult to test the relative merits of these 

 assumptions by experiment, for on my view, when two races of Dutch 

 are crossed, raonohybrid inheritance ratios are to be expected (3:1 in 

 F2, 1:1 in back-crosses), but on Punnett's view dihybrid or trihybrid 

 ratios are often to be expected. If with this point in mind the reader 

 will examine my Text-figure 1^ in which are summarized the data on 

 crosses between two of the Dutch races studied (viz. Dark and White), 

 I think he will be convinced that the inheritance is unmistakably mono- 

 hybrid. Punnett does not attempt to apply in detail to this cross his 

 three-factor hypothesis. If he did, I think that hypothesis would be 

 found to fail completely. This cross is, of all those made, least affected 

 by minor genetic factors (" residual heredity "), since the two races 

 crossed were originally isolated from the same stock and may thus be 

 supposed to have had most minor genetic factors in common. 



Punnett offers three specific objections to the interpretation of this 

 case as involving a single pair of (major) allelomorphic factors. Each of 

 these objections rests on a misapprehension of the facts, 



1, The first objection is that the "Dark" race is not homozygous (in 

 major factors) because too variable. In reality the variation curve for 

 the uncrossed Dark race is steep, monomodal, and nearly symmetrical. 

 It is based on 172 carefully graded progeny all by the same sire. It is 

 the smoothest variation figure of those obtained for any of the Dutch 

 1 Carnegie Inst. Wash., Publ. No. 288. 



