Abstract
The genetic mode of warfarin resistance in Rattus rattus was studied by crossing experiments of resistant and susceptible colonies. The configuration of the selected colony, [RR]・F_1,was estimated to be [5/10 RR+3/10 RS+2/10 SS] from the plateaux on the log day-probit mortality curve. The log day-probit mortality line of the RR, or homozygous resistants, was estimated from the high mortality portion of the [RR]・F_1 curved line. The [RS]・F_1 colony was obtained by crossing the [RR]・F_1 with the Amami Colony, which is considered to be a homozygous susceptible colony (hereinafter referred to as SS). Theoretically, the [RS]・F_1 colony should be a mixed population of [13/20 RS+7/20 SS]. The theoretical curve thus calculated was similar to the observed curve. Accordingly, the estimated straight line for the RS, or heterozygous hybrids, was established. The [RS]・F_2 colony obtained by crossing [RS]・F_1×[RS]・F_1 should theoretically be a mixed population of [169/1,600 RR+702/1,600 RS+729/1,600 SS]; and the backcross [RRS]・F_1 colony obtained by crossing [RR]・F_1×[RS]・F_1 should theoretically be a mixed population of [169/800 RR+442/800 RS+189/800 SS]. The theoretical curves for the above two were compared with the observed curves. The observed curves were similar to the corresponding theoretical curves, except in respect to the high mortality portions. The reason for the discrepancy at the high mortality portion was not clear. Through these results, warfarin resistance in R. rattus was concluded to follow the mode of monofactorial Mendelian resistance; and from the locality of the RS line, the resistant gene should be incompletely recessive. The discriminating date should preferably be the 28th day, because the survivals on that date should be only the homozygous resistants, thereby enabling easy calculation of the RR ratio in any population concerned.
