Abstract
Sera from house mice of eight laboratory strains and three feral populations have been examined for esterase activity by means of starch-gel electrophoresis. In one of the feral animals (a pregnant female) a modification in the first anodal band (esterase I) was observed. Results obtained from mating the progeny of this female were consistent with the hypothesis that the appearance of this first esterase band is under the control of a pair of autosomal alleles, lacking dominance. The locus has been designated Es-2 with alleles Es-2a and Es-2b. Evidence was obtained which suggests that the esterase I component is not a member of an isozymic group.