HEREDITY 



well as in wild rats, mice, squirrels, and other 

 rodents. In this type of coat reddish yellow 

 pigment alone is found in a conspicuous band 

 near the tip of each hair, while the rest of the 

 hair bears black pigment. The result is a 

 brownish or grayish ticked or grizzled coat, 

 inconspicuous, and hence protective in many 

 natural situations. 



Some red individuals produce the reversion 

 in half of their young by black mates, some 

 in all, and others, as we have seen, in none, 

 this last condition being the commonest of the 

 three. It is evident that the reversion is due 

 to the introduction of a third factor, additional 

 to simple red and simple black. It is evident 

 further that this new third factor, which we 

 will call A (agouti), has been introduced 

 through the red parent, and that as regards 

 this factor, A, some individuals are homozy- 

 gous (AA) in character, others are heterozy- 

 gous (transmit it in half their gametes only), 

 while others lack it altogether. Further ob- 

 servations show that it is independent in its 

 inheritance of both black and red; it is in 

 fact an independent Mendelian character, which 



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