374 



The Journal of Heredity 



Example 



lai White pattern (roan 



type) roan cattle 



la2 White pattern (pie- 

 bald type) Dutch rahlnt 



laa Dilution of all colors 

 (maltese and li^ht 

 red type) hluc rabbit 



lb Dilution of all colors 

 (sepia and cream 

 type, albinism) dilute ^'winea- 



2ai Yellow pattern (ag- 

 outi type) Kra>' rabljit 



2a2 Yellow pattern (tor- 

 toise type) tortoise guinea- 

 pi K 



2a3 Density of black 



(sooty type) sooty rabljil 



2b Dilution of black 



only (brown type)., .brown mouse 



While the lines between these classes 

 especially between 2a2 and 2a3 cannot 

 be drawn very closely, most factors are 

 readily placed. 



In the discussions of the different 

 mammals, a list is given of the Men- 

 delian factors which have been thor- 

 oughly demonstrated in the opinion of 

 the writer. They are classified accord- 

 ing to their apparent physiological effects 

 under the scheme above. The effect is 

 given in more detail by a brief descrip- 

 tion of the color variety which differs 

 by only the unit factor in question 

 from a certain ty]je, that of the wild 

 species, where this is known. The 

 color of a variety which differs from the 

 type by more than one factor is easily 

 deduced in all cases. Thus a mouse 

 which differs from the gray color f)f 

 wild mice only by factor s is a ]3iebal(l 

 gray, by factor b is a cinnomon gray in 

 which the l:)lack jjarts of the fur are 

 changed to brown, while a mouse which 

 differs by both is naturall\' a piebald 

 cinnamon. Where the two factors are 

 in the same class, a double effect is 

 l^rodviced. Thus a mouse like the wild 

 in fonnula except for factors p and b 

 has a (Umble dilution of black, the black 

 ])arts of the fur becoming xcvy ])ale 

 brown. 



No wholly satisfactory system of 



s}-mbols for Mendelian factors seems 

 yet to have been devised, and there is 

 little uniformity among authors. Where 

 only a pair of allelomorj^hs is known, 

 the present ])a]jer follows the con- 

 venient s\'stem of rej^resenting the 

 dominant factor by a cajjital, the 

 recessive by a small letter. The same 

 letter with different subscripts is used 

 for sy.stems of multiple al]elomori)hs. 



THE FACTORS OF MICE 



In many respects mice have been found 

 to be better adapted for exix^rimental 

 work than any other mammal. From 

 the first they have attracted a great 

 number of investigators, among whom 

 first jjlace must be given Cuenot- 

 whose work has had a most profound 

 inlluence on genetic theory apart from 

 its bearing on inheritance in mice. 

 The results are in harmony on most 

 points and the essential facts may be 

 considered as very thoroughly estab- 

 lished. Seven sets of Mendelian allelo- 

 morphs, as listed above, have been 

 identified. At least two important 

 series of \'ariations do not seem to 

 follow simi)le Mendelian inheritance 

 and ha\-e so far defied analysis. 



ICxeluding the second jnebald factor, 

 each of the other six sets of allelomorphs 



^Cudnot, L. 1902-11. Arch. Zool. F.xp. el G6n. {?>), 10; (4), 1, 2, 3, 5, 6, 8. 



