The Gametophyte Factors of Maize

Abstract

While there are a number of loci in maize that are specifically expressed in the gametophytic generation (e.g., lethal ovulel and 2, small pollen, etc.) that are gametophyte factors in the broad sense of the term, maize geneticists use the term to refer specifically to the numerous loci designated as gametophyte factor (ga). At all but one of these loci, pollen grains carrying a Ga allele have a pronounced competitive advantage in effecting fertilization over pollen carrying the ga allele on the silks of plants that are Ga/Ga or Ga/ga but not on the silks of ga/ga plants. In some instances, the competitive advantage may be nearly complete. The exception to this generalization is ga7 on chromosome 3, where the competitive advantage of Ga gametes over ga is only slightly influenced by the genotype of the silks in which they are growing (Rhoades 1948). The ga7 locus thus differs from the other ga factors to be discussed, and the ga7 allele may be a hypomorphic mutation at a locus whose product is required for pollen tube growth.