374 ANIMAL BIOLOGY 



attain results in experimental breeding of the greatest 

 practical value. 



Let us see what this law is. In crossing varieties of peas 

 that differed in certain well-defined characters Mendel 

 found that in the first generation the offspring were not 

 intermediate in respect to the characters in question, but 

 that one character was represented apparently to the com- 

 plete exclusion of the other. Thus crosses of tall and 

 dwarf peas produced nothing but tall peas, and crosses of 



x 



E 



FIG. 247. Mendelian inheritance in Guinea pigs. A black animal, 

 A, mated with an albino, B, produces progeny which are all black like C. 

 These progeny have albinism in a recessive state, and when they are mated 

 produce blacks, D, and albinos, E, in the ratio of three to one. 



yellow with green peas produced only peas that were 

 yellow. The character such as tallness or yellowness 

 which appeared to the exclusion of its opposite was called 

 dominant, the suppressed character being called recessive. 

 The most striking results, however, were obtained in the 

 second generation after the members of the first generation 

 were crossed with one another or self -fertilized. The reces- 

 sive character was then found to reappear in one-fourth of 

 the progeny, the other three-fourths showing the dominant 



