-u^^ 



Fig. 50. 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 i)arcnt, but showing traces of the recessive white spotting. Note while left fore foot. F;, the four 

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

 hooded. Numerically aii 9 : 3 : 3 : 1. Let the reader identify iu Table 12 the uuit-characters involved. 



