Breakup of Initial Linkage Blocks Through Intermating in a Cotton Breeding Population1

Restricted character recombination was observed in the F2 generation of a cross between two contrasting inbred lines of cotton. If initial linkage blocks were an important cause of the restricted recombination, intermating for several generations should break up such linkages and increase genetic recombination. Beginning with the F2 generation, the population was maintained for six successive generations in an isolation block where the natural mating system was mixed intermating and selfing (approximately 50% self‐pollination). The population was resampled to study the effects of intermating on genetic recombination for seven quantitative traits. Genotypic variances decreased for six traits for which coupling‐phase linkages would be expected to predominate and increased for one trait for which repulsion linkages might have been more important. Genotypic correlations between traits tended to shift toward values observed in populations assumed to be more nearly at linkage equilibrium. These observed changes conform with expectations that intermating dissipates initial linkage diseqilibrium. Changes in gene frequency which occurred during intermating for some of the traits, however, confounded the interpretation of the observed results.