To facilitate the use of the semigamy trait for chromosome manipulations and crop improvement, the time and mode of gene expression was examined. A novel statistical approach utilizing joint-scaling tests was devised for genetic analysis. Initially, a genetically-marked set of parents was mated in a 3X3 factorial design to produce nine progeny seed populations. These populations were subsequently evaluated to determine the relative frequencies of maternal and paternal haploids, and chimeras for each. Semigametic frequencies were then analyzed by joint-scaling tests based on a genetic model consisting of maternal additive and dominant, paternal additive and dominant, zygotic additive and dominant, megagametophytic, and microgametophytic genetic source effects. Chi-square tests of the genetic effects model implied that the semigamy gene was qualitatively inherited. Joint-scaling tests and associated t-tests indicated that the semigamy gene was being expressed at the sporophytic level as an incompletely dominant allele. Maternal influence was strong whereas paternal influence was moderate. Our results exemplify a new method for analyzing genetic control of certain types of apomixis.