SS Experimental Zoology 



"pure" race was not pure, since it may produce some albinos 

 when paired with albinos. 



Allen has also carried out a large number of experiments with 

 mice. Crossing the gray house mouse with the albino gave 

 gray offspring, as most other experimenters have found. The 

 second generation {F^ gave approximately the Mendelian ratio 

 of three grays to one white, the former being partly pure grays, 

 partly mixed. Crossing the dominant recessives (heterozygote) 

 with the extracted albinos, where equality of grays and whites 

 would be expected, gave 84 pigmented young and 64 whites. 

 While there is only an approximation to equality here (74 of 

 each expected), the deficiency in white may be due to insuf- 

 ficiency of numbers, but possibly to some other factor. Allen 

 found that when spotted mice were bred to albinos the oft*- 

 spring were spotted, — often with less white than the original 

 spotted parent, — and in some cases the white almost, or even 

 completely, disappeared. Thus, although we may look upon 

 the spotted condition as a unit-character that is dominant, its 

 extent appears to be variable. In fact, a latent character may 

 also come to light here that is not seen in either parent, but must 

 be potential in one or in both of them. While the white parent 

 might have been expected to add more white to the offspring, — 

 on Galton's hypothesis, — the result is exactly the opposite. 



When pigmented, heterozygote individuals {F^ were inbred, 

 they produced 159 pigmented young and 55 albinos (53.5 being 

 the Mendehan expectation). In another experiment, pig- 

 mented, heterozygote individuals {F^ were bred to pure albi- 

 nos, giving 69 pigmented and 69 albinos, exactly the anticipated 

 ratio. 



Allen carried out a number of experiments made to test the 

 inheritance of partial albinism, as he calls the condition when 

 white areas are present along with colored areas. When "par- 

 tial albinos" are bred to pure albinos, the young {F^ were more 

 nearly totally pigmented (as stated above), some showing no 

 trace of white, others had white toes, or a white tip to the tail 

 or even a few scattered white hairs. One only had a white spot 



