38 



LABORATORY MOUSE 



the normals and of the chinchillas will carry extreme dilution 

 and half will carry albinism. 



Gametes 



Gametes 



Zygotes 



If these hybrid-generation animals be mated at random 

 four kinds of germ cells will be formed in equal numbers and 

 will unite also at random, producing on the average 7 normals, 

 5 chinchillas, 3 extreme dilutes, and 1 albino. Of the 7 nor- 

 mals, 1 will be pure bred, 2 will carry chinchilla, 2 will carry 

 extreme dilution, and 2 will carry albinism. Of the 5 chin- 

 chillas, 1 will be pure bred, 2 will carry extreme dilution, and 

 2 will carry albinism. Of the 3 extreme dilutes, 1 will be 

 pure bred, and 2 will carry albinism. The 1 albino will be 

 pure bred. See diagram. 



Gametes 

 C c ch c H c 



Gametes 



Suppose we have a mouse bearing two independent unit- 

 characteristics (borne in different chromosomes), for ex- 

 ample, rodless and albinism. The determiner for the albino 

 character lies in one chromosome pair and that for rodless 

 in an entirely different pair. The genetic formula of this 



