94 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



zygotes AaBb. The females would be unaffected, but the males would 

 be sterile on account of the disturbances between A and a, and 

 between B and b. Mating the fertile females, which likewise have 

 the zygotic formula AaBb, back to the guinea-pig, aabb, would give 

 the following: 



AaBb J wild females. 



AB + Ab + aB + ab | wild eggs. 



ab + ab tame sperm. 



r25 p. et. fertile males. 



AaBb + Aabb + aaBb + aabb ... | wild zygotes \ 75 p. ct. sterile males. 



[lOO p. ct. fertile females. 



This hypothesis would explain the absolute sterility of some j wild 

 males (AaBb), but also admit of a further maturation or tendency to 

 fertility in those individuals with less disturbing combinations, i. e., 

 with more factors from the tame (Aabb and aaBb). The ultimate reces- 

 sive, aabb, would be fertile and would occur in 25 per cent of the cases. 

 Now, if the numbers were large and the different zygotic classes of 

 I wild females were' represented in about the expected proportions 

 given, then 56.25 per cent of the F3, or | wild males, would be fertile. 

 One could not distinguish the different classes of F2 females by inspec- 

 tion, but the random mating to guinea-pig males would be symbolized 

 as follows: 



AaBb + Aabb + aaBb + aabb \ wild females. 



AB + 3Ab + 3aB + 9ab \ wild eggs. 



ab + ab tame sperm. 



("56.25 p. ct. fertile males. 



AaBb + 3Aabb + 3aaBb + 9aabb. . 5 wild zygotes j 44.75 p. ct. sterile males. 



[100 p. ct. fertile females. 



Here again, if the numbers were large and the different zygotic classes 

 of females were represented in the expected proportions, then 76.56 

 per cent of the yVwild males should be fertile; and, in any generation, 



(2°~^— -1\ ^ 

 1 — j males should be fertile (n being the number of the hybrid 



generation). 



Table 77 likewise gives the most probable percentages of fertile males 

 expected in each generation from the Fi through the Fg on the basis 

 of two factors, it being supposed that the females of any generation 

 are distributed in the expected proportions of the different zygotic 

 classes. 



The most probable percentages of fertile males, the ultimate recessives 

 in the different generations on the basis of various numbers of factors, 

 from 1 to 9, are given in table 77. The general scheme will be evident 

 from an examination of this table, for, stated in simple manner, the 

 percentages of fertile males would be as given in table A. 



