36 A MANUAL OF MENDELISM 



In Miss Durham's third experiment, agouti was mated 

 with blue, and their hybrids' progeny were agoutis, 

 dilute agoutis, blacks, and blues in the ratio 9:3:3:1. 

 The characters carried by three of these groups are 

 already known, and, if we set down the four groups 

 forming the set in the usual order with the known 

 characters against the groups to which they belong, we 

 shall be able to infer the characters carried by the 

 remaining group : 



Agouti XYZ 

 Dilute agouti 



Black xYZ 



Blue xY z 



Since it is carried by three of the groups in the set, Y 

 must also be carried by the fourth. The differentiating 

 characters in the set are therefore X and x and Z and z ; 

 and, since three of the four possible combinations made 

 by these characters are already appropriated, the 

 remaining combination, Xz, must belong to dilute 

 agouti, whose three characters are thus XYz. 



In Miss Durham's last experiment, cinnamon-agouti 

 was mated with silver-fawn, and their hybrids' progeny 

 consisted of cinnamon-agouti, dilute cinnamon-agouti, 

 chocolate, and silver-fawn in the ratio 9:3:3:1. If 

 we again arrange the four groups in the usual order 

 with the characters of the three groups which are 

 known set down against them, we shall be able to infer 

 the characters belonging to the fourth : 



Cinnamon-agouti XyZ 



Dilute cinnamon-agouti 



Chocolate x yZ 



Silver-fawn x y z | 



i 



