A Gametophyte Factor on Chromosome 5 of Corn.

Received December 28, 1960 A REVIEW of the early studies of the gametophyte factor (ga) on chromosome 4 of corn was presented by EMERSON (1934), when he published his data and discussion on this interesting pollen character. In certain female stylar tissue, the ga pollen that effects fertilization is reduced from the expected 50 percent to a mere 0-4 percent if it is competing with pollen carrying the dominant allele. More recently SCHWARTZ (1950) suggested that a third allele (Gas) is at the ga locus of chromosome 4. NELSON (1952) studied this multiple-allelic series and reports that the reaction between the diploid style and the ga haploid pollen-tube, when competing with pollen tubes carrying a dominant allele, may be relative rather than absolute. He feels that environment may be one of the factors that serves to influence the progress of the competing pollen tubes down the stylar tissue. BURNHAM (1936) found that chromosome 5 in certain corn strains showed differential fertilization. Since this publication, his students have obtained data to show that other chromosomes carry ga factors. These data have been presented in the Maize News Letter as their studies progressed. Gametophyte factors such as those on chromosomes 4 and 5 of corn have certain characteristics that make their transmission difficult to follow. Even the detection of a ga factor requires that it be linked with a factor with a visible effect. The presence of a ga factor in the stock of translocation #5614, which has breaks near the centromeres of chromosomes 5 and 9, was detected in 1954. Later studies of this translocation demonstrated that the ga factor was on chromosome 5.