Full text: Problems in eugenics

70Exhibit M 2—3 
M 3All the rabbits are homozj'gous for th2 black factor B. 
Homozygous agouti = AA BB EE. 
Black rabbits may be either :— 
(1) Rabbits of the constitution aa BB EE. These breed true and 
behave as simple recessive to agouti. 
(2) Rabbits of the constitution AA BB EE I')D., i.e., agoutis to which 
a double dose of D has been added are pure blacks in appearance, 
when only a single dose of D is added the animal shows some 
agouti markings and is an agouti-black. Such rabbits have always 
proved to be heterozygous, and when mated together give blacks, 
agouti-blacks, and agoutis in the ratio 7:6:3. 
(3) Rabbits of the constitution AA BB Ee Dd. An agouti-black 
(AA BB EE Dd) becomes a pure black when heterozygous for E. 
Such blacks when mated with blacks of constitution aa BB EE dd 
throw some agoutis and also some agouti-blacks. 
Further, the experiments have shewn that the factor D is coupled 
with E in the gametogenesis of rabbits of the constitution AA BB Ee Dd. 
The gametes produced by such animals are of two kinds only viz— 
ABED and A B e d. When mated with a tortoise aa BB ee dd they 
give blacks and yellows only—and no agoutis. So far as is known, the 
coupling between E and D is complete. At present this is the only 
case of coupling between characters yet worked out in a mammal. 
Experiments with Poultry, illustrating the recombination of 
characters.Brown Leghorn $ 
(a) Coloured (chiefly brown) 
{&) Normal feathersor (a) White plumage (with 
without slight buff tinge) 
(/>) Silky feathers 
(n) Coloured 
(à) Normal feathers 
F2 Generation 
Coloured plumage Coloured plumage White plumage White plumage 
Normal feathers Silky feathers Normal feathers Silky feathers

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