INHERITANCE OF WHITE-SPOTTING IN RABBITS. 19 



The foregoing observations show unmistakably that the several 

 members of this allelomorphic series tend, as a result of crosses, to 

 become more like each other. This has been described as mutual 

 modification, but it should be expressly stated that in the light of 

 our experiments with rats "modification" need not be regarded as 

 change in the nature of a single gene, but merely as equalization of the 

 residual heredity additional to the single genes which produce mono- 

 hybrid ratios. 



ENGLISH. 



In November 1909 there were received at the Bussey Institution 

 four " English" rabbits, 1 male and 3 females, bred by R. W. Wills, 

 of Hornerstown, New Jersey. In terms of the grading scale shown in 

 plate 3, the male was of grade 2-j-; the females were of grades 2, 2-f, 

 and 3, respectively. 



In matings of the male with each of the 3 females, there were pro- 

 duced both English and self-colored young, as shown in table 30; 

 of the former, 21 ; of the latter, 8. The self young were later found to 

 produce no English young when bred inter se. Hence it seems clear 

 that English is a dominant Mendelian character, that self is recessive 

 in relation to it, and that the 4 English parents were all heterozygous 

 dominants. 



The question now arose whether homozygous English rabbits could 

 be produced and why English rabbits were not regularly bred in 

 homozygous form. We did not have long to wait for an answer to 

 these questions. Table 30 shows that the English young of our 4 

 original English rabbits fall into two groups quite different in appear- 

 ance. Of the 15 young which were graded, 5 were of grade 1 or 1^, 

 while 10 were similar to the parents in grade, varying from grade 2 

 to 3. The group of low-grade English was found to consist of homo- 

 zygous individuals which produced only English young in crosses 

 with each other or with selfs. The higher-grade group, twice as num- 

 erous in individuals, was found to consist of heterozygotes. These 

 are preferred by the fancier because of their much more striking color- 

 pattern. The homozygote is in appearance only an impure white 

 animal, but the heterozygote is beautifully mottled. It is therefore 

 clear why the fancier breeds heterozygotes. (See plate 3.) 



Our original English buck, 2545, was also mated with self-colored 

 does of several different sorts, viz, gray, cream, yellow, sooty yellow 

 (tortoise), black, and black-and-tan. In regard to color inheritance, 

 these matings gave us such results as are already familiar through 

 earlier publications by Punnett, Hurst, and ourselves. We may 

 therefore confine our attention to the behavior of the English pattern 

 in crosses. Table 30, B, shows the results obtained; 26 English and 

 18 self young were recorded from these matings. No grade was 

 recorded for 17 of the English young. The others varied in grade 



