Sex Determination in Maize

Maize (Zea mays) is a classic example of a monoecious plant: separate male and female flowers develop on the same individual rather than on separate plants. The terminal inflorescence, which develops from the shoot's apical meristem at the very top of the plant, bears the staminate (male) florets and is called the tassel, while the lateral inflorescence, which develops from an axillary bud lower on the stem, bears the pistillate (female) florets and is called the ear or cob. This separation of sexes within one plant is achieved developmentally by the selective abortion of the stamens in the ear florets and of the pistils in the tassel florets. Two single-gene substitutions determine whether that normal selective-abortion programme runs correctly or is disrupted: the allele ba (for 'barren plant'), when homozygous, eliminates the silk and ear entirely and makes the stalk purely staminate, while the allele ts (for 'tassel seed') transforms the tassel into a pistillate structure that produces no pollen. Combining these two genes gives four distinct outcomes: the double recessive ba/ba, ts/ts plant lacks silk on the stalk but has its tassel transformed into a pistil, giving a rudimentary female; the ba/ba, ts+/ts+ plant lacks silk but keeps a normal tassel, giving a functional male; the double dominant ba+/ba+, ts+/ts+ plant develops both a normal tassel and a normal cob, giving the standard monoecious plant; and t …