Rat kappa-chain allotypes

The presence of rat kappa-chain allotype specificities (RI-1a and b) has been studied in 13 subspecies of the seven native Australian species ofRattus. RI-la reactivity was not detected among these rats. On the other hand, extensive cross-reactivity was seen with RI-1b, some sera cross-reacting totally (R. leucopus cooktownensis), some not at all (R. colletti), and the remainder showing at least two distinct levels ofpartial cross-reactivity, confirming the existence of multiple specificities for Rl-lb. Three subspecies show polymorphism with respect to Rl-lb cross-reactivity (R. sordidus, R. colletti, andR. l. leucopus) and in one case (leucopus) breeding studies have indicated that there is allelic inheritance of this trait. The segregation of RI-1b reactivity has been studied in crosses and backcrosses made between species differing in their RI-1b reactivity, and the results are consistent with the existance of codominant alleles at a single locus. The fact that these species differ extensively in their karyotype opens the door to possible chromosomal localization of this and other genetic traits.