The present study was carded out at Sakha Agricultural Research Station, during the two winter wheat-growing seasons; 2004/2005 and 2005/2006. Six bread wheat genotypes namely; Gemmiza 9, Irene, Sakha 61, Line 1, Line 2 and Line 3 were used. These genotypes were crossed in a half diallel mating design to determine the genetic mechanism controlling earliness and grain yield characters. The parental genotypes and their E_l's were planted in a randomized complete block design with three replications. The studied characters are: days to heading, days to physiological maturity, grain filling period, plant height, number of spikes/ plant, number of kernels/ spike, kernel weight, grain yield/ plant and grain filling rate/ plant. The results revealed that the additive and dominance gene actions were significant for most of the studied characters. Additive gene action played the major role in the inheritance of all studied characters. The mean degree of dominance (H_ilt)) ⁱⁿ for all characters were less than one confirming the role of partial dominance gene effects in controlling the traits. The "F" values coupled with KD/KR ratio, indicated excess of dominant increasing alleles for all studied characters except for number of days to maturity, plant height and number of kernels/ plant Narrow-sense heritability estimates were relatively high for all characters, indicating the importance of additive gene action.