Mr Doncaster, On the Inheritance of Coat-colour in Rats. 221 



albino (expectation 1 in 4). The expected ratio of self-brown, 

 pied brown, self-black and pied black respectively is 9 : 3 : 3 : 1 ; 

 the actual numbers 12, 0, 4, 2. In this experiment I bred the 

 only brown without white (type 1) which I have obtained. 



In Exp. 23, where a half-wild was mated with a black-and- 

 white containing recessive albino, the numbers approximate to 

 the Menclelian expectation, viz. 15 coloured to 6 albino (expecta- 

 tion 15 : 5) ; and the four colour types 5:4:2:4 (expectation 

 equality). 



A point of some interest is the great diversity of different 

 litters from the same pair. Where enough offspring are reared 

 the results are in fair accord with Mendelian expectation, but in 

 individual litters this is often far from being true. To save space 

 the separate litters are not recorded in the tables, but examples 

 can be given. In Exp. 23 ( $ alb. x <£ blk.-wt.) the first litter 

 consisted of 5 albinos, 1 " Irish," 2 brown (type 2) ; the second 

 litter of 1 albino, 4 " Irish," 2 brown. In Exp. 37 ( % alb. x £ blk.) 

 three successive litters contained respectively 5 albino, 2 " Irish," 

 1 brown ; 3 albino, 1 " Irish," 2 brown ; 1 albino, 3 Irish, 1 brown. 

 And in Exp. 44 (alb. % x " half-wild " <f) four successive litters 

 consisted of 2 albinos and 6 coloured, 7 albinos and 1 coloured, 

 3 albinos and 4 coloured, 7 albinos and 3 coloured, the total 

 making up 19 albinos to 14 coloured. 



It is evident from such facts that a large number of young 

 must be reared from each pair before the true proportions are 

 known with any accuracy, and unfortunately disease has killed 

 off many of my rats before this could be done. 



