The Waxy Locus in Maize. I. Intralocus Recombination Frequency Estimates by Pollen and by Conventional Analyses.

T H E waxy (wx) locus in maize conditions the type of starch which is synthesized in the triploid endosperm and in the haploid pollen grain. Further, the phenotype of a pollen grain is determined by its own genotype and not by that of the plant which produces the pollen grain (BRINK and MACGILLIVRAY 1924) and (DEMEREC 1924). This makes it possible to use the pollen grain as the unit of observation in genetical investigations on the wx locus. The W x pollen grains stain blue with an iodine-potassium iodide stain while wx pollen grains stain a reddish-brown color. Since a maize plant produces millions of pollen grains, large populations can be obtained and scored easily, thus markedly enhancing genetic resolution. The investigation of low frequency events is more easily carried out with this system than with any other locus in a higher organism (NELSON 1957). The test for intragenic recombination at the locus is to cross two wx mutants of supposedly independent origin, collect pollen from the F, plant, and score the frequency of Wx pollen grains. A frequency significantly above the mean of the Wx frequencies in the parental stocks may well be indicative of genetic recombination between two different sites of mutation which reconstitutes a functional W x locus. It has been shown in a set of the ten all-combination crosses between five wx mutants that seven F, progenies show such significantly higher Wx frequencies (NELSON 1959). Thus, for this locus in maize, recombination within the functional unit between different mutant sites has been substantiated. The purpose of this paper is to report that the Wx frequency estimated for a cross ( wxgO times wxCoe) by pollen analysis is similar to the W x frequency estimated for the same cross by conventional genetic techniques and to record the segregation of outside markers in the Wx recombinants. Further, the results from backcross progenies are in agreement with the hypothesis that heterozygosity for mutant alleles at the wx locus is a prerequisite for high Wx frequencies. The W x frequency estimated for the pollen grains produced by the cross between any two wx mutants should be similar to the Wx frequency for the same cross estimated in a backcross to a w x / w x female parent. In attempts to check this particular point the F, Bz wxgoV,/bz wxGoe u1 was used. The frequency of