Six bread wheat genotypes namely Giza164, Giza168, Sidsl, Sids7, Sahka93 and Debeira were used to study. The inheritance of grain yield and its components i.e. number of spikes/plant, number of kernels/spike and kernels weight, using a half-diallel cross in the F1 and F2 generations. The parental genotypes, F1 hybrids and F2 populations were grown in a randomized complete block design with three replicates under normal and Late sowing conditions (heat stress). Results exhibited that late sowing reduced number of spikes/plant, number of kernels/plant, kernels weight and grain yield/plant by (13.17 and 11.65 %), (11.76 and 7.50 %), (9.98 and 15.78%) and (21.82 and 27.27 %) for FI and F2 generation, respectively as compared with normal planting date. The best parents under the two sowing dates were Debeira for number of spikes /plant, Skis 7 for number of kernels /spike and kernels weight, Sids 1 for grain yield and Sakha 93 under the recommended planting date. The most promising F2 populations in grain yield were (P1xP3), (PixPe.), (P3xP6) and. (P.,x1,5) under normal conditions. Heat stress index values showed that the heat tolerant parents were Sids 7, Giza 164 for number of spikes/plant, Sids 1 and Debelra for number of kemels/spike, Sids 1 for kernels weight and Sids 7 for grain yield. The promising F2 populations for heat tolerance were (P1xP6), (PixPs), (P2xPs) and (P2xP3) and selection could be practiced in these populations for grain yield and/or its components. Both additive and non-additive gene effects were important in the genetic system for yield and its components. The additive gene effects were the most prevalent type under both sowing dates for these characters except for grain yield in F1 under late sowing and in F2 populations under both sowing dates. The parents showed more positive alleles for all traits in both generations under both sowing dates except for kernels weight in the Fr and F2 generations under recommended planting. Broad-sense heritability values varied from intermediate to high in all characters. Narrow-sense heritability values intermediate to low in all characters. These results indicate that these characters could be affected by dominance effects and environmental factors. From the previous results we can conduded that selection in segregation generation could be effective to produce lines have high grain yield under heat stress.