CHAPTER VIII 



MENDEL'S LAW OF HEREDITY ILLUSTRATED IN 



ANIMAL BREEDING 



Mendel's law may best be explained with the aid of ex- 

 amples, which will be chosen, for convenience, from the 

 heredity of guinea-pigs. If a guinea-pig of pure race with 

 colored fur (say black) is mated with a guinea-pig having 

 uncolored (white) fur, a so-called albino, the offspring will 

 all have colored fur, none being albinos. See Figs. 27-30. 

 To use Mendel's terminology, colored fur dominates in the 

 cross, while albinism recedes from view. Colored fur is, there- 

 fore, called the dominant character; albinism, the recessive 

 character. 



But if now two of the colored individuals produced by this 

 cross are mated with each other, the recessive (albino) 

 character reappears on the average in one in four of their 

 offspring (Fig. 30). The reappearance of the recessive char- 

 acter, after skipping a generation, in the particular propor- 

 tion, one fourth, of the second generation offspring, is a 

 regular feature of Mendelian inheritance. It may be ex- 

 plained as follows (see Fig. 30a) : the gametes which united in 

 the original mating of a pure colored individual with an 

 albino must have transmitted, one color (C), the other 

 albinism (c) . The contrasted characters were then associated 

 together in the offspring. But color from its nature domi- 

 nated, since albinism is due apparently to the lack of some- 

 thing necessary to the formation of color, which the other 

 gamete would supply. 



But when the young produced by this cross have become 

 adult and themselves form gametes, the characters, color and 

 albinism, will separate from each other and pass into differ- 

 ent gametes, since, as regards the transmission of alternative 



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