ALLKN. — THE HEREDITY OF COAT COLOR IN MICE. 157 



gamete with which it unites. In support of this hypothesis, it has been 

 found that these bhick animals, on being back-crossed with chocolate 

 mice, produce nearly equal numbers of black and of chocolate young. 



The gray heterozygotes resulting from the cross of chocolate with 

 albino mice, when interbred, did not produce the expected one-in-four of 

 cliocolate mice, but instead golden-agouti and black young were more 

 numerous than those of the chocolate color, and these three classes were 

 together alxnit one-fourth as numerous as the gray. This result is prob- 

 ably due to a resolution of a portion of the gametes of the albinos having 

 the gray character, so that black-chocolate and golden-agouti are present 

 in different gametes. A similar resolution is also indicated by the back- 

 cross of one of the gray heterozygotes with the chocolate })arent, for the 

 resulting olfspring represented the gray, the black, and the golden-agouti 

 types, but not the chocolate. 



(3) Golden-agouti mice, characterized by having the yellow and the 

 chocolate pigments, breed true to their type as a rule, but may give 

 the chocolate type also. Chocolate as well as golden-agouti mice may 

 be obtained by crossing the two types, but it is not yet certain whether 

 this result is due to a resolution of the color of the golden-agouti or 

 whether the latter contains chocolate in a recessive condition. 



A cross of golden-agoutis with albino mice coming of mixed ancestry 

 (including gray) resulted for the most part in gray young, though one 

 golden-agouti female produced two l)lack young, when bred to such an 

 albino. These latter probably indicate that the female was producing 

 some gametes with the chocolate character, which, uniting with the 

 gametes from the all)ino having the black character, gave black young. 

 This hypotliesis is supported by the fact that the two black young bred 

 inter se gave both l)lack and chocolate offspring, and so must have been 

 heterozygous with respect to the two pigment-characters. The albinos 

 used were of a stock known to produce a proportion of gametes having 

 the black character. 



The gray young, resulting from this cross of golden-agouti with albino 

 mice, gave, when interbred, about one-fourth of golden-agouti offspring, 

 indicating that that character became segregated at gamete formation. 

 P^xcept for a single black young, the other progeny were gray. 



Back-crossing the gray heterozygotes witli golden-agouti animals re- 

 produced the two types only, but the grays were present in slightly more 

 than their expected proportion, although the total number of young was 

 not large. 



(4) In general, therefore, unresolved gray is dominant over all of the 



