In this experiment, the means of the six populations (of each of two bread wheat crosses; Mexipak × Acsad-8 and Ipa-99 × Attla were used to estimate gene effects, component of variance and heterosis for some quantitative traits viz: Plant height, days to heading, flag leaf area, spike length, spikes/plant, grains no./spike, biomass yield/plant, grain yield/plant and harvest index. These generations were produced during two growing seasons, 2009-2010 and 2010-2011. The generations were grown in

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... Randomized Complete Block Design with six replications at the Research Field of the College of Agriculture, Salahaddin University, Erbil, Iraq. Genetic analysis was performed using the joint scaling test based on three and six parameter models. The results revealed that inheritance of the traits could not be explained by additive-dominance model. Additive and dominance gene effects were significant for most traits in both crosses due to different origins of the parents. The values of (dominance × dominance) were greater than (additive × additive) and (additive × dominance) of most studied traits in both crosses in addition to greater values of dominance gene effect than the additive in most traits. It was suggested that selection all of them should be effective in advanced segregating generations due to epistatic gene effects. High narrow and broad sense heritability (0.94) was obtained for flag leaf area in Mexipak × Acsad-8 cross, while high narrow sense heritability (0.86) and high broad sense heritability (0.98) were obtained for spike length and flag leaf area in Ipa-99 × Attla, so the early generation testing and selection might be recommended for these traits. Heterosis was found to be positive for most traits in both crosses.