60 



INHERITANCE IN RABBITS 



BLUE-GRAY. 



A blue-gray rabbit differs from a gray one only in the intensity of its 

 pigmentation, which is always dilute. As regards the intensity factor, 

 therefore, it is invariably homozygous, D2, since D is recessive to I, whereas 

 a gray rabbit may be either homozygous, 1^, or heterozygous, I (D). Con- 

 sequently only half as many zygotic combinations are possible among blue- 

 gray as among gray rabbits, 16 instead of 32 being the maximum. 



The 16 conceivable varieties of blue-gray rabbits, all of which should 

 be similar in appearance but different in breeding capacity, are: 



(i) Blue-gray producing only blue-gray; formula, B2Br2E2A2C2D2U2Y2. 



(2) Blue-gray producing blue-gray, and blue; formula, B2Br2E2AC2D2U2Y2. 



(3) Blue-gray producing blue-gray, and white; formula, B2Br2E2A2CD2U2Y2. 



(4) Blue-gray producing blue-gray, blue, and white; formula, B2Br2E2ACD2U2Y2. 



(5) Blue-gray producing blue-gray, and cream; formula, B2Br2E(R)A2C2D2U2Y2. 



(6) Blue-gray producing blue-gray, blue, cream, and pale sooty; formula, 



B2Br2E(R)AC2D2U2Y2. 



(7) Blue-gray producing blue-gray, cream, and white; formula, 



B2Br2E(R)A2CD2U2Y2. 



(8) Blue-gray producing blue-gray, blue, cream, pale sooty, and white; formula, 



B2Br2E(R)ACD2U2Y2. 



The 8 remaining varieties would be identical with these, except for the 

 factor U, in which they would be heterozygous, U (S), producing spotted 

 as well as self-pigmented young. 



Three blue-gray rabbits, all females, have been tested, and each of 

 these is of a different zygotic formula. 



Female 389, the original blue-gray individual, proved to be of variety 

 4. When mated with <? 248, a black animal heterozygous in E, C, and 

 I, i. e., of formula B2Br2E(R)CI(D)U2Y2, she produced gray, blue-gray, 

 blue, and white young, all the expected classes except black being produced. 

 The observed numbers of the young and the expected proportions are 

 given in table 39. 



Table 39. 



Female 656 was of variety 2, heterozygous in A only, as is shown by 

 table 40. 



Of the 4 males with which 9 656 was mated, all but c? 1340 produced 

 albino young in other matings. This indicates clearly that 9 656 was 



