830 S])oUing in Mice and their Genetic Behaviour 



"Daruma" (1 ? and 5cf cT) coming from the cross "Kasuri"x"Daruma" 

 and its reciprocal, and also six " Kasuri " (1 $ and 5(^) coming from the 

 cross " Kasuri " x " Kasuri," were tested for this purpose, but it was found 

 none of them were homozygous as to the D factor. If these numbers 

 are added to those obtained in the case of " Daruma " x " Daruma," the 

 total is fifty-four in number. The evidence strongly supports the view 

 that the mice homozygous for D invariably perish at the embryological 

 stage. On this assumption the consequence of the modified ratio 2 : 1 of 

 D : d, which resulted from the cross Dd x Dd, can be clearly understood. 

 The case is similar to that of the yellow mice. 



Both the, factor for the yellow coat-colour and the D factor have a 

 dominant effect upon the somatic character, but act recessively on the 

 lethal result. Analogous cases have been reported by Bridges (1916), 

 Metz (1916) and others in Drosophila, and Vilmorin (1914) in Triticum. 

 Apart from mice no other similar case has been described in rodents. 



The " English " pattern in rabbits is, however, characterized by fine 

 silvered markings of spotting like that of the " K&,suri " race in mice. 

 According to Castle and Hadley (1915) the homozygous animals of this 

 race are quite capable of existence, but have a slightly spotted coat or, 

 as they called them, " Whiter-than-standard." So the factor for the 

 " English " pattern has no influence upon the viability of the animal, 

 even when it is doubled, though the pattern development of this race 

 and the epistatic nature of the factor for the " English " upon the self 

 resemble those in mice. 



In studying rats the v;^riters once bred a number of the dark-eyed 

 ones, including, besides pure whites, some slightly spotted ones in 

 a fashion similar to the variation among the " Daruma " race in mice. 

 Unfortunately, however, this experiment had to be abandoned before 

 data sufficient to report were in hand. 



In guinea-pigs there are dark-eyed whites sometimes found. Accord- 

 ing to Castle (1905) the genetic behaviour of this type seems to be 

 complex. 



Extracted Self and Piebald. 



Extracted selfs and piebalds from crosses where D occurs transmit 

 their characteristics by the usual ways as follows : If the homo- 

 zygous selfs extracted are crossed with pure piebalds the resulting 

 young are all selfs. By two matings of this sort, six animals having 

 self-coloured coat were born. When the heterozygous extracted selfs, 

 however, are mated to piebalds, the two sorts of young result in almost 



