234 Coat-Colour in Rabbits 



At the same time five black (/'j/' bred similarly to the above black 

 % % were also tested. Of these one turned out to be homozygous for A, 

 two turned out to be heterozygous, while the remaining two did not 

 cany A. In all therefore 18 blacks from the mating of agouti-black 

 X yellow were tested for the presence of A, and as the subjoined list 

 shews the proportion of those homozygous for A, heterozygous for A, 

 or homozygous for its absence tallies closely with expectation : 



AA Aa aa 



Proportion found by testing ... 4 6 8 



Proportion expected 3'6 7 '2 7'2 



The test of the coupling between D and E. 



The possession of a number of agouti- bearing blacks renders possible 

 the carrying out of a critical test to decide whether the suggested 

 coupling between D and E occurs. On this hypothesis the gametes 

 produced by the agouti-bearing black are DEA, DEa, deA, dea if it 

 is heterozygous for A, and DEA, deA if it is homozygous. Such 

 animals when mated with yellows or tortoises should be able to give 

 yellow offspring hut no agouti. And as one of the parents in such a 

 mating lacks the factor E, no agouti-blacks should appear from such 

 matings. In Table IX are shewn the results of crossing the agouti- 

 bearing black % $ with a heterozygous yellow (^ {E 31). Hitherto 

 from such matings have come 15 blacks, 16 yellows, and 7 tortoises, 

 but no agoutis or agouti-blacks. A few families have also been raised 

 from agouti-bearing black ^^^ and tortoise $ ?, viz. : 



Black Agouti Yellow Tortoise 



c?28 X tortoise ? 3 — 1 2 



<?54 X ,, $ 7 — 3 — 



<?20x„? 2 — 3 — 



<?20 X orange ? 3 — 8 — 



In all there have been raised from the mating of agouti-bearing 

 black with either yellow, tortoise or orange, 64 young\ Of these 30 

 were black, 25 yellow, and 9 tortoise. No agoutis and no agouti-blacks 

 have appeared from such matings. These results, as has already been 

 shewn, are explicable on the hypothesis of coupling between the two 

 factors D and E. On the explanation suggested, and with such facts 

 as are at present available, the coupling must be supposed to be com- 

 plete. Analogy with cases of possibly similar nature in the sweet pea 

 and other plants suggests that the coupling, though intense, may yet 

 be but partial. Larger numbers however are necessary before a decision 



1 Excluding Himalayans. 



