38 Inheritance of Coat-Cotour in Rabbits 



factor A however behaves in segregation independently of D and E- 

 Owing to this coupling no animal contains D unless it also contains E, 

 and no animal which is heterozygous for E can be homozygous for D. 

 In other words, if the coupling is complete, animals of the constitution 

 DDee, Ddee, and DDEe should not be found. 



The presence or absence of D makes no difference in the appearance 

 of a rabbit which contains E, but lacks the agouti factor, A. Whether 

 D is present or not such animals are normal blacks. But when A 

 is present in animals homozygous for E their appearance differs 

 according as they are homozygous or heterozygous for D. When 

 heterozygous the animal is mainly black with a slight sprinkling of 

 agouti hairs, which are most numerous at the back of the neck (of. 

 Journ. Gen. 1912, PI. XII, fig. 2); when homozygous it must be 

 supposed to be full black'. Further, the aj)pearance of an animal 

 containing both D and A differs according as it is homozygous or 

 heterozygous for E. If homozygous it is an agouti-black : if hetero- 

 zygous it is a normal black in appearance. 



Hence the zygotic constitutions of animals containing D, E, and A 

 are limited to the following: 



1. DDEEAA 



2. DDEEAa 



3. DdEEAA 



4. DdEEAa 



5. DdEeAA 

 (3. DdEeAa 



normal black, 

 agouti-black, 

 normal black. 



At the time when the earlier results were given in 1912, all of the 

 above six classes had been experimentally identified with the excep- 

 tion of the first. As the identification of these different classes is 

 critical for the hypothesis adopted, experiments were begun in order 

 to find the animal of the constitution DDEEAA. It was shewn that 

 when agouti-blacks of the constitution DdEEAa were bred together 

 they gave, as the hypothesis demanded, blacks, agouti-blacks, and 

 agoutis closely in the ratio 7:6:3. Such animals produce the four 

 types of gamete, DEA, DEa, dEA, dEa, and the results of two such 

 gametic series meeting is shewn in the subjoined scheme : 



' Critical evidence in favour of tbis view was lacking in 1912 but has since been 

 obtained (p. 39). 



