All the rabbits are homozygous for the 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 DD., 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—A B E D 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.