In soybeans, there are at least four recessive genes (ms1, ms2, ms3, ms4) that impart unconditional male sterility. A plant homozygous for any of these genes sets seed almost exclusively as a result of pollen transfer from male-fertile plants. A consequence of male sterility is that seed from sterile plants tends to be larger than those from fertile plants (Burton et al., 1979; Carter et al., 1983).