UNIT-CHARACTERS (GENE MUTATIONS) 25 



Those yellows which contain a non-agouti gene (a) are 

 often sooty yellow (see Fig. 18) in appearance, and have 

 sometimes been called "sables" (47, 54)- 



Chocolate yellows are clearer in color than those contain- 

 ing black, i.e. have a less sooty appearance. 



Reds (A Y A, or Y Y a plus darkening modifiers) 



These animals of the fancy are a dull red, similar in color 

 to Rhode Island Red fowls. 



Genetically they are lethal yellows with intensifying modi- 

 fiers. They breed as yellows, but the complete genetics of the 

 modifiers has not yet been worked out, although Dunn (46) 

 has studied it extensively and has shown that it must be 

 considered as due to numerous modifying genes. 



Dominant spotting (IF) (broken spotting) 



A mouse with the hair pattern of a leopard. — Eh Yah, c. 1100 B.C. 



This variety (see Fig. 21) is characterized by the presence 

 of small irregular broken spots or polka-dot patches of color 

 upon a white ground. In higher grades pigmentation per- 

 sists about the eyes and dorso-caudal region only. 



Dominant spotting (112, 162, 53, 72) is expressed, as the 

 name indicates, in animals containing but one dose of the 

 gene. Homozygotes die of anaemia at an early age, under 

 eighteen days (37, 40). Fancy breeds of this type are known 

 as black-eyed whites (see Fig. 23). They contain one domi- 

 nant-spotting gene and two recessive-piebald genes, i.e. are 

 heterozygous for dominant spotting and homozygous for 

 recessive piebald. In some strains, perhaps all, pure-breds 

 (homozygotes) are inviable. Dominant spotting may be 

 due to localized inhibitors for the tyrosin-tyrosinase reaction. 

 This type of spotting has come to us from Japan. In Chinese 

 history it is recorded that in 120 b.c. (or more probably 

 a.d. 40) a wise court official who was able to recall the name 

 of this variety was rewarded by the Emperor with a cartload 

 of silken textiles. 



