CROSSES OF CAVIA CUTLERI. 



15 



was supposed in advance to involve 4 independent Mendelian factors, a 

 supposition which the observed result justifies. The factor differences 

 in the two races are: gametes of cutleri, ABCE; of albino (race C), abce. 

 On this hypothesis the Fi hybrids should form 16 different kinds of gam- 

 etes, the color potentialities of which are indicated in parentheses: 



From this list it will be observed that 2 different gametic factorial 

 combinations are capable of producing black-eyed yellow, and that 

 the same is true concerning brown-eyed yellow, while 8 different com- 

 binations contain the potentialities of albinos. From these considera- 

 tions it follows that the F 2 ratio will be peculiar, since each of the yellow 

 classes that can be distinguished from each other (black-eyed and 

 brown-eyed) will itself be composite, and the same will be true of the 

 albino class. The expected classes and their proportional frequencies 

 will accordingly be : 



Golden agouti 81 



Black 27 



Cinnamon 27 



Yellow (black-eyed) 36 



Yellow (brown-eyed) 12 



Chocolate 9 



Albino 64 



A cross involving the formation of so many classes of individuals can 

 not be expected to show very satisfactory Mendelian ratios in so small 

 a number of offspring as 44. All the expected classes are represented, 

 although black is represented in a single individual only. 



The colored individuals of race C were known in many cases to carry 

 albinism as a recessive character. The albino gametes of such indi- 

 viduals would, in crosses with cutleri mates, form the same kind of 

 zygotes as the albinos of race C, which were used in the cross just 

 described. In considering the results of such crosses, it is therefore 

 proper to include in one category Fi animals derived from both sources. 

 If this is done the F 2 young are increased to 108, distributed as shown 

 in table 7, the expected theoretical number in each class being shown in 

 a parallel column. 



Table 7. 



