314 The Genetics of the Dutch Rabbit 



Further data of Castle's are those obtained by mating ^i animals 

 with a White Dutch {Text-fig. 2, p. 11). The 116 offspring fall into 

 two groups without overlapping, each containing 58 individuals. On 

 the hypothesis of multiple allelomorphs we should have expected the 

 group with greater pigmentation to have shewn a distribution of grades 

 similar to F^ animals. As a matter of fact the mean grade is 5-6, and 

 the range between 1 and 9, whereas in the F^ animals the range is only 

 1-3, with a mean about 1'5. So also in the light groups the range is 

 13-17 as against that of 15-17 in White Dutch, while the mean is about 

 15 as against between 16 and 17 in White Dutch. This extension of the 

 ranges and shifting of the means of the two groups is however what is 

 to be expected on the interpretation I have suggested. Making use of 

 the grades assigned in Fig. 2 to the various genetic constitutions 

 involved, I have worked out the distribution of the progeny for this 

 cross, as shewn in Table II. Here again, as in the case of the F^ 

 generation, the hypothesis I have suggested appears to fit the facts 

 better than that of multiple allelomorphs with its necessary concomitant 

 of " mutual modification." 



TABLE II. 



Grades 12 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 



Calculated ) , j^ j^ jq 5 iq 5 5 - — _ — — 10 10 15 17 7 

 Distribution \ 



Actual ) 

 distribution I 2 3 4 11 11 14 9 3 1 _ — _ — 1 14 24 13 6 

 from Castle ) 



(2) The cross between Dark Dutch and White Dutch (pp. 8-10). In 

 this cross five $ $ of grades 6-8 were mated with a*</ of grade 17. 

 The majority of the offspring were of grades 5-9 {Text-fig. 1, p. 9), 

 though two were of grades 10 and 11 respectively. As both of these 

 were from the same doe ( $ 6666, Table 22) it suggests that she may 

 have been heterozygous for P, while the other four were homozy- 

 gous. A true F2 generation was apparently not raised, but animals 

 of grades 4-9, variously produced and known to throw the White 

 Dutch form, were bred together. The 56 progeny resulting varied 

 between grades 1-17. They may be divided into two groups, (a) 

 with a range between grades 1-10, and (b) a smaller group with a 

 range of 12-17. The mean grade of (a) is higher (i.e. less pigmented) 

 than that of the dark strain as a whole, while the mean of (b) is 

 lower than that of the white strain as a whole. In other words the 

 two groups into which this " F2 " generation falls approximate more 

 closely to one another than do the parental dark and white groups 



