A male-sterile mutant, mei-1, of Arabidopsis thaliana is described. In
this mutant, instead of a tetrad of four microspores being formed aft
er meiosis, a ''tetrad'' consisting of from five to eight microspores
is formed. The microspores show a wide range of sizes and of DNA conte
nts. The mutant is female-fertile. This mutant was produced by seed tr
ansformation with Agrobacterium and appears to be T-DNA tagged.