36 



LABORATORY MOUSE 



a sperm) to form an embryo, the double number is again 

 restored. 



A pure-bred gray-coated mouse receives a determiner for 

 pigment development (C) from its father and one from its 

 mother. When its gametes are formed, each will contain 

 a single pigment determiner. Hence, in matings with 

 another pure-bred gray, a pair of pigment determiners will 

 enter into each embryo and nothing but pure-bred pigmented 

 young will be produced. 



In like fashion an albino receives one determiner for 

 albinism (c) from its father and another from its mother, and 



Fig. 6. Diagram illustrating the inheritance of a simple, recessive, mendelizing unit-character 

 such as albinism. Black wafer = C gene, white wafer = c gene. 



produces gametes each bearing a determiner for albinism. 

 Thus, when two albinos are mated together their offspring 

 will receive a determiner for albinism from each parent and 

 hence all are albinos. 



If an albino is mated with a pure-bred gray, the albino 

 will contribute an albino determiner (c) and the gray will 

 contribute a pigment determiner (C) (see Fig. 6). It so hap- 

 pens that the pigment determiner in this case completely 

 dominates over the albino determiner and the cross-bred 

 offspring are pigmented, giving no evidence that they carry 

 an albino determiner. A cross-bred gray carrying albinism 

 produces two kinds of germ cells in equal numbers, half 



