This study was carried out at in the Agricultural Experimental Farm of Alexandria University during 1996 – 98 seasons. The main objectives of the study were determing the genetic effects that control yield, yield components, plant height and silking date in maize. Two crosses were used for applying Gamble model (1962). One of the two crosses represented early maturing parents, whereas, the second included full season parents. Data from parents, F₁, F₂, BC₁ and BC₂ were used in the analysis. The main results of the study were; Heterotic effects were positive and significant for most characters in both crosses except for silking date in both crosses and ear height in cross II relative to the high parent, over-dominance was responsible for heterotic effects of grain yield and its components in both crosses. Negative heterotic effects were found for silking date suggesting fruitful selection for earlier hybrids from in these populations. Dominance effects were significant  for most characters except for, silking date in cross II. Also, additive effects were significant except for ear height in cross I. Epistatic effects were found responsible and significant for most of the studied traits. Heritability estimates for all studied characters ranged between high estimates for grain yield/plant, ear length, ear diameter and ear height in both crosses through moderate estimates for plant height and 100 – kernels weight in cross II to low estimates for silking date in cross I. Estimates of heritability were reflected on expected genetic advance from selection within F₂,.The present estimates of genetic gain of selection are expected to be higher than anticipated due to the presence of epistasis. However, they showed that the selection would be effective in improving grain yield in both populations. The first cross is recommended for the breeder interesting in developing high yielding earlier synthetics.