Fig. 56. A dihybrid Mendelian cross between a wild Norway rat and the tame variety known as 

 black hooded. P, parents; wild gray at left, black hooded at right. Fi, a heterozygote, gray like the 

 wild parent, but showing traces of the recessive white spotting. Note white left fore foot. F;, the four 

 second-generation classes of offspring. From left to right, gray self, gray hooded, black self, black 

 hooded. Numerically as 9 : 3 : 3 : 1. Let the reader identify in Table 12 the unit-characters involved. 



