THE AMERICAN NATURALIST 



[Vol. LIV 



yellows (PPrr), the p and R of the pink-eyed and the P 

 and r of the red-eyed tended to be linked, the crossing 

 over being about 17 or 18 per cent. 



More recently Castle (1916) has given evidence indi- 

 cating that Irish pattern (Si), entirely pigmented except 

 for a white patch on the belly, is allelomorphic to both self 

 (S) and the hooded pattern (Sn). Whiting and King 

 (1918) have shown that the non-yellow condition (CV) 

 corresponds to that found in guinea-pigs and is similarly 

 allelomorphic to both complete pigmentation (C) and 

 albinism (Ca).. Dilute pigmentation (Ca) has not as yet 

 been found in rats. Castle (1916) presents experimental 

 proof that the allelomorphs of pink-eyed (p) and red- 

 eyed (r), or P and R, are linked with albinism, Ca. This 

 would put the three genes on the same chromosome. 

 Castle's data are too few for the exact degree of link- 

 age to be determined from them. 



Up to the present no results have been published of a 

 direct attempt to determine the possible linkage relations 

 of self (S) and agouti (A) to each other or to the other 

 three linked genes. Data bearing on this point will be 

 presented in this paper. It will also be shown that so far 

 as our evidence goes the genes R and Ca are absolutely 



The first crosses made were for the purpose of deter- 

 mining the linkage relations of the red-eyed pair of allelo- 

 morphs (R and r) with the self series (S, Si and Sn). 

 Eed-eyed selfs (rSPa) were crossed with black-eyed 

 hooded (RSi,Pa) and the resulting animals were there- 

 fore self 2 -blacks (rS-RSn). 3 These self-blacks were then 

 bred back to the double recessives, red-eyed hooded 

 (rrShSh). The offspring from this mating are shown in 

 Table I. From this it will be seen that red-eyed and self 

 are entirely independent in heredity. 



^ With my animals every heterozygous self (SS h ) had a white patch on 

 the belly. 



3 P and a may be disregarded since both parents were alike with respect 

 to these genes. 



