66 



THE AMERICAN NATURALIST [Vol. LIV 



The albinos from this mating when mated to their red- 

 eyed yellow litter mates, or to red-eyed yellows from sim- 

 ilar matings, should give nothing but black-eyed blacks 

 (RCa-rC). This would prove for both albinos and red- 

 eyed yellows that each was the result of the union of two 

 non-crossover gametes. The black-eyed blacks when 

 mated together should behave just like their black-eyed 

 black parents, i.e., produce all three phenotypes. In this 

 case also this would prove that two non-crossover gametes 

 had united in the production of each black-eyed black 

 parent. 



The above policy has now been pursued for some time. 

 From the mating together of RCa-rC black-eyed blacks 

 the following offspring have resulted : 



23 albinos, 57 black-eyed' blacks, 31 red-eyed yellows. 

 For some reason there is a deficiency of albinos. As 

 previously explained, black-eyed blacks may be distin- 

 guished at birth from either albinos or red.-eyed yellows 

 by the color of their eyes. In the above cross five animals 

 died early, but none of them were black-eyed. They died 

 before one could be sure whether they were albinos or 

 red-eyed yellows. If there was selective mortality, and 

 they were all albinos, the deficiency of albinos would thus 

 be explained. 



So far 13 albinos from RCa-rC X RCa-rC matings have 

 been tested and all proved to be RC a RC a ; therefore they 

 are the result of the union of 26 non-crossover gametes. 

 Similarly, 12 .black-eyed blacks proved to be RCa-rC and 

 10 red-eyed yellows, rC rC. The total number of non- 

 crossover gametes going into the production of the above 

 animals is 70, and is at least a fair indication that R and 

 Ca are completely linked. More results are necessary in 

 order to make this conclusive. Since the amount of cross- 

 ing-over between R and P is already known (17-18 per 

 cent.), and since R and C a are completely linked, we 

 should expect to find the same percentage of crossing- 

 over occurring between P and Ca as between P and R. 



