Previous studies have identified wheat (Triticum aestivum L.) chromosome substitution lines between 'Cheyenne' (CNN) and 'Wichita' on, that contain quantitative trait loci (QTLs) affecting yield and yield components, anthesis date, plant height, and grain volume weight. However, chromosome substitution lines can only identify additive or epistatic gene action. In this study, hybrids between CNN and WI, and between chromosome substitution lines and their recurrent parents were evaluated in four field environments to determine if the QTLs exhibited additive and dominant gene action which could result in heterosis. As expected, the chromosome substitution lines were significantly different for grain yield from their recurrent parents, which indicated the chromosomes contained additive genes. Three of four chromosome substitution line hybrids were not different from the midparent value, which indicated predominantly additive gene action. However, the fourth substitution line hybrid significantly differed from the midparent value for grain yield, which indicated the chromosome contained genes that were heterotic and had dominant gene action. Some hybrids did not significantly differ from one parent, which further indicated the possibility of dominant gene action. Midparent heterosis also was identified in the cultivar hybrid for grain yield. High parent heterosis was not found for any of the measured traits. Hence, genes on these chromosomes exhibited predominantly additive gene action, but also exhibited dominant gene action which may explain some of the heterosis found in the cultivar hybrid.