[Competition between the male gametophytes in Oenothera under the influence of a gametophytic gene in the first linkage group and a model for investigations of branched genetic maps].

The progeny ratios obtained in male backcrosses of Oenothera hybrids to the complexes hookeri and flavens (identified by two marker genes and by the translocation break) showed statistically significant differences from Mendelian expectations.Presence of a gametophytic gene in the first linkage group is proposed. Its alleles ga (+) and ga (-) are thought to control development of the male gametophytes in such a manner that pollen grains carrying the different ga alleles and developing in a heterozygous female plant, will fertilize the female gamete with different average frequencies.A series of genetic models is developed, all taking into account the relative probability of the alleles ga (+) and ga (-) to function in fertilization, the probability of crossing over between the gene loci studied, and the branched configuration of the linkage group, due to the presence of the translocation.Based on these models, the relationships between the relative frequencies of the different classes of gametes are predicted for several theoretically possible arrangements of the genes within the linkage group.The models have general application for the localization of gametophytic genes and for the localization of genes in branched linkage groups.It turns out to be impossible to give an estimate for the disadvantage of ga (-) as compared to ga (+) from the backcross data alone. The empirical data permit only a combined estimate of the probabilities of fertilization by ga (-) and of crossing over between Ga and the locus of the marker gene.Comparison between the empirical data and the model makes it possible to determine the location of the marker loci and the locus of Ga with respect to one another. A branched linkage group appears most likely, but a linear arrangement in two chromosome arms cannot be ruled out.The observed cross-over values, and consequently, the map distances between the genes studied, are highly variable, both in different hybrids and in the progeny of a single hybrid.