32 



INHERITANCE IN GUINEA-PIGS. 



the pink-eye variation with colored coat, first brought to the attention 

 of scientists in the case of mice through the experiments of Darbishire 

 (1902). A similar variation has, however, since been found to occur 

 in rats (Castle, 1914) . The number of factors in which d 1 1002 is hetero- 

 zygous is surprisingly large and implies doubtless considerable cross- 

 breeding in the guinea-pig colonies kept by the natives of Arequipa, a 

 fact perhaps connected with the great size and vigor of their animals. 

 The factorial constitution of cfl002, as at present understood, is as 

 follows: 



(1) Agouti factor, Aa, agouti-marked but transmitting non-agouti as a recessive 



character. 



(2) Black factor, BB, homozygous. 



(3) Color factor, CaCr, two different recessive variations, dilution (Cd) being 



dominant over red-eye (C r ). Both are recessive to ordinary intense color 

 (C) and dominant over albinism (C a ), the four forming a series of quadruple 

 allelomorphs, as shown by Wright (1915). 



(4) Extension factor, EE, homozygous. 



(5) Dark-eye factor, Pp, heterozygous for the recessive pink-eye (p) variation, 



with which goes dilution of black or brown pigments, but not of yellow. 



(6) As regards the rough variation, this animal is smooth, but nevertheless trans- 



mits occasionally a trace of the rough character, but the character does not 

 crop out among his descendants in any as yet recognizable Mendelian 

 proportions. 



(7) White spotting, homozygous. 



(8) Yellow spotting, homozygous. 



TABLE 19. Classification of young obtained from matings of &1002 with unrelated guinea-pigs. 



Male 1002 was mated with 20 dark-eyed guinea-pigs and 6 albinos 

 derived either from race B, from a 4-toed race (see Castle, 1906), or 

 from crosses between the two. Both these races contain only non- 

 agouti animals. The dark-eyed mothers produced 70 FI young, the 

 albino mothers produced 18 F! young. Disregarding spotting with 

 yellow and with white, the young of the dark-eyed mothers fall into 

 three classes dark-eyed intense, dark-eyed dilute, and red-eyed and 

 each class may be further subdivided into agouti and non-agouti. (See 

 table 19.) 



The albino mothers, though derived from the same races as the dark- 

 eyed mother, produced only two of the three main classes of young, 

 viz, dark-eyed dilute and red-eyed, which fact confirms Wright's (1915) 



