RUBY-EYED DILUTE GRAY RAT 57 



the dilute rats carry the agouti and the self factors. Seven litters 

 of Fo rats were obtained, which contained forty-seven individuals, 

 twenty-three males and twenty-four females. Of these individ- 

 uals eight males and ten females were of the wild gray type; 

 two males and three females were black; six males and three 

 females were dilute gray; two males and three females were gray 

 hooded; three males and two females were black hooded; one male 

 and two females were dilute gray hooded, while one male and one 

 female were dilute black or light sepia. The fact that hooding 

 and non-agouti appeared among the dilutes shows that dilution 

 segregates independently of these characters. There were in all 

 thirty-three intense and fourteen dilutes, which is close to the 

 expected ratio. 



Dilute males crossed with albino females sired twent}^ litters 

 consisting of one hundred and thirty-one individuals, seventy- 

 three males and fifty-eight females. These were all distinctly 

 lighter in color than the wild dilutes and appeared to be inter- 

 mediate between ruby-eyed dilutes and albinos. We have called 

 them fawn-colored. The fact that the cross with the Albino 

 has failed to reconstitute the wild type indicates that the new 

 dilution factor is allelomorphic with albinism, except for the im- 

 probable assumption that simplex albinism has reversed the dom- 

 inance of ruby-ej^ed dilution. If the latter were the case, we 

 should expect the F2 generation to show some intensely pigmented 

 mdividuals by recombination of factors, but as none of these ap- 

 peared it is evident that the new dilution factor is allelomorphic 

 with albinism. The Albino females used in this experiment were 

 homozygous for black, or non-agouti, and for hooding. Wright 

 ('17 c) has discussed the new dilution factor. We may follow 

 his nomenclature and call self S and hooding Sh ; agouti A and 

 black a; intense pigmentation Cr, ruby-eyed dilution Cr, and 

 albinism Ca. Thus expressed, the cross is dilute gray SS. 

 AA. CrCr X Albino ShSh.a a.CaCa = all fawn-colored SShAa.CrCa. 

 The expected proportion in the F2 generation would be nine dilute 

 grays, three dilute blacks or light sepias, three dilute gray hooded, 

 one light sepia hooded, twenty-four fawns (agouti and non- 

 agouti), eight fawn hooded, and sixteen Albinos. In sixteen lit- 



