80 



THE INHERITANCE OF COLOR IN MICE. 



It has been shown, then, that yellows of the four dark-eyed intense pigmented types exist. 



The pink-eyed yellows (types XXI-XXIV inclusive) have been crossed only inter se or with 

 black pigmented forms, but it is certain that they also can occur in the four types com- 

 parable to the dark-eyed intense series. 



The dark-eyed dilute yellows have been crossed with brown only in a few cases. Chiefly 

 they have been bred inter se to determine whether the 2 : 1 ratio holds good in their 

 case as in the intense forms. Of those tested, one, 9 7298, is of the zygotic formula 

 YiBriBdiPpAiU and when crossed with a pink-eyed brown has given 1 yel, 1 pdyel, 

 1 BAg, 2 BrAg, 1 vBAg. This shows that types XXV and XXVII can exist. The 

 other animal, also a female, gave by a pink-eyed brown male, 7 yel, 2 pyel, 2 Blk, 2 Br, 

 3 pB. This animal was of the formula YiBriBd^PpB, and argues strongly in favor of 

 the existence of types XXVI and XXVIII. 



Of the pink-eyed dilute yellows few have been tested, but I have, at present, a race of animals 

 which give only two sorts of young, viz, pink-eyed dilute yellows and pink-eyed dilute 

 browns; such pink-eyed dilute yellows are the ultimate recessives of the yellow series 

 belonging to type XXXII, formula YiBr2di'p2R- 



From the few matings given above, together with the larger number of yellow matings which 

 follow, it is easy to see that yellows may be obtained of the various zygotic compositions 

 found in the non-yellow varieties, differing from them only by the addition of the restric- 

 tion factor, R. 



We shall first consider the crosses between yellow animals of these four varieties, which form 

 the intense dark-eyed series. 



Yellow X yellow, giving only dark-eyed intense young. 

 Cross 102. Giving Y and Br. 



Cross 103. Giving F, Br, and W (and in one case BrAg). 



