Wilson — Simplified Solutions of Certain Mendelian Problems. 483 



differ from the first in more tlian two pairs of characters and from the two 

 middle groups in more than one : — 



9 X Y 



3 X y 



3 j; Y 



1 X u Z. 



The experiments dealt with first in the previous paper were those carried 

 out by Miss Durham on the colours of mice. It will be convenient to 

 consider them first again, and to consider two other important examples 

 after. The details of Miss Durham's experiments are to be found in the 

 fourth " Report to the Evolution Committee of the Royal Society " and in 

 the first volume of the " Journal of Genetics." 



In Miss Durham's first experiment, agouti-coloured mice were mated with 

 chocolates, and their hybrids' progeny consisted of agoutis, cinnamon 

 agoutis, blacks, and chocolates in the ratio 9:3:3:1. Bince there are 

 2- (i.e. 4) groups numerically in the ratio (3 + 1)^ there are two pairs of 

 characters concerned ; and, since the effects of the factors producing them are 

 inseparable, the four groups can only be set down witli "unknown" symbols, 

 thus : — 



Agouti, ^ X Y 



Cinnamon agouti, . . . 3 X y 



Black '6 X Y 



Chocolate, 1 •» 2/ 



In Miss Durliam's second experiment, black was mated with a fifth 

 colour, silver fawn, and their hybrids' progeny consisted of blacks, blues, 

 chocolates, and silver fawns in the ratio 9:3:3:1. By being at the top 

 of a set of four groups black is shown to be carrying two dominants. One 

 may be Y, revealed in the first experiment, but both may be new. Assume 

 that both are new. Tlien the characters carried by the four groups in the 

 second experiment should be, say — 



Black, . . . . '^ Z A 



Chocolate o Z a 



Blue, . . . . ?. % A 



Silver fawn, . . . 1 z a. 

 In that case the characters carried by black and chocolate, as revealed 

 by the two experiments, should be — 



Black, . . . . X Y Z A 



Chocolate, . . . x y Z a. 



4g2 



