Genetic exchange in mixed populations of differentially marked strains of the soil bacterium B. subtilis growing in soil culture lead to marked changes in gene and genotypic frequencies. The same results were obtained with additional, fully isogenic, strains. The dynamics of this phenomenon in 1 pair of strains were examined by manipulating starting inoculum sizes, ratios of strains in starting inocula and nutritional conditions. The populations rapidly reached equilibrium with respect to total numbers and numbers of the final dominant recombinant phenotype, and the combination of traits carried by the final dominant phenotype depended on the starting frequencies of the parent strains, on environmental (nutritional) conditions, and possibly on interactions between genetic loci.