ABSTRACT
Zea mays, or maize, belongs to the grass family, a large group of angiosperm species. Most grasses do not exhibit sex determination and, as such, develop perfect flowers. Maize is monoecious, developing male and female flowers in different locations on a single plant. A description of grass flowers and how flowers are arranged in inflorescences (Dahlgren et al., 1985) in the grass family is helpful in understanding sex determination in maize. Grass flowers are simple and inconspicuous, lacking sepals and petals. A typical grass flower consists of a bract-like organ called a palea, a whorl of two or three lodicules (possible petal homologues), three stamens, and a tricarpellate, unilocular pistil, containing a single ovule. The flowers of all grasses are borne multiply in complex inflorescences, the basic unit of which is the spikelet. A spikelet is a short branch that consists of one or more flowers, each subtended by a bract called a lemma, and the entire spikelet is enclosed by a pair of so-called sterile bracts, the glumes. Spikelets can be indeterminate, having many florets (flower plus lemma), a primitive condition in the Gramineae, while determinate spikelets, with only a few florets, are regarded as a more advanced character. Maize belongs to the tribe Andropogoneae, all of whose members have determinate, two-flowered spikelets (Clayton, 1986). The subtribe to which maize belongs, the Maydeae, in addition to having determinate spikelets, also is entirely monoecious (Kellogg and Birchler, 1993). Sex determination in maize is most advanced among the members of the Maydeae, having segregation of male and female flowers into separate inflorescences in distinct locations, the terminal tassel and the lateral ears (Dellaporta and Calderon-Urrea, 1994; Irish, 1996; Veit et al., 1993).
