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).
Carter, T. E. Jr.; Burton, J. W.; and Huie,Jr., E. B.
"Research Notes : United States : Mechanical separation of seed from male-sterile and fertile plants by seed size,"
Soybean Genetics Newsletter: Vol. 11
, Article 48.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol11/iss1/48