Effect of Inbreeding of Parental Lines on Predicted Yields of Synthetics 1

Some plant breeders have suggested that high yielding S 1 parental lines should produce a higher yielding synthetic variety than low yielding highly inbred lines of equal combining ability. These breeders, using Wright's formula, drew conclusions from comparisons of hypothetical yields of synthetics produced from n S 1 lines and n highly inbred lines. The correct comparison should be n S 1 lines vs. 2 n highly inbred lines. It can be shown that Wright's formula predicts yields of synthetics regardless of the degree of inbreeding of the parental lines, and the yield of a synthetic is dependent only on the gene frequency of the parental lines. Parental lines which yield high because of low inbreeding will produce a synthetic equal hi yield to a synthetic produced from low yielding highly inbred lines if the gene frequency of the highly inbred lines equals the gene frequency of the less inbred lines.