Estimation of gene action through partioning of genetic variance was carried out, using the parents, F1, F2 and F3 populations in the cross Giza 90 x Pima S62 (24202). Results showed that the heterotic effects relative to better parent (useful heterosis) were positive and highly significant or significant for all studied characters except for First Fruiting Node (FFN), boll weight (BW), micronair value (Mic), Fiber strength (St) and Fiber elongation (Elon %), while days to first flower (DFF) recorded highly significant better parent heterosis value. Mid-parent heterosis values were highly significant and negative for days to first flower (DFF) and boll weight (BW). On the other hand, the remaining traits revealed positive and highly significant or significant heterotic effects except for First Fruiting Node (FFN), lint percentage (L %), micronair value (Mic) and Fiber elongating (Elon %) which showed insignificant heterotic effects. Inbreeding depression was positively significant and highly significant for all traits except for boll weight (BW), micronair value (Mic) and Fiber elongation (Elon %). On the other hand First Fruiting Node (FFN) and days to first flower (DFF) recorded negatively significant inbreeding depression. Regarding potence ratio, partial dominance values were obtained for all studied traits except for days to first flower (DFF), seed cotton yield/plant (SCY/P), lint yield/plant (LY/P), Fiber strength (St) and upper half mean length (UHM) which recorded over dominance. Concerning the type of gene effects, the additive gene effects were negative and highly significant for days to first flower (DFF), Fiber strength (St) and upper half mean length (UHM), while lint yield/plant (LY/P), lint percentage (L%) and Fiber elongation (Elon %) showed positive significant and highly significant for additive gene effect. Dominance gene effects were positive and highly significant or significant for days to first flower (DFF), seed cotton yield/plant (SCY/P), lint yield/plant (LY/P), Fiber strength (St) and upper half mean length (UHM) and boll weight (BW), respectively. On other hand, Fiber elongation (Elon %) trait showed highly significant negative dominance gene effect. Additive x additive gene type of epistasis effects were highly significant for seed cotton yield/plant (SCY/P), lint yield/plant (LY/P) and lint percentage (L%), while first fruiting node (FFN), days to first flower (DFF), boll weight (BW), micronair value (Mic), Fiber strength (St), uniformity index (UI), upper half mean length (UHM), seed index (SI) and lint index (LI) recorded negatively highly significant and significant epistatic of gene effects. With regarded to the dominance x dominance interaction, the values were positive and highly significant for all studied traits except for seed index (SI), lint index (LI) and uniformity index (UI). High values of broad sense heritability (over 50%) were detected for first fruiting node (FFN), boll weight (BW) and Fiber elongation (Elon %). Moderate heritability estimates (between 30% and 50%) were found for seed cotton yield/plant (SCY/P), lint yield/plant (LY/P), seed index (SI), lint index (LI), micronair value (Mic), uniformity index (UI) and upper half mean length (UHM). Low broad sense heritability values (less than 30%) were obtained for days to first flower (DFF), lint percentage (L %) and Fiber strength (St). Narrow sense heritability estimates were calculated for lint index (LI), Fiber strength (St), uniformity index (UI) and upper half mean length (UHM), which exceeded 50% value. Moderate heritability estimates were observed for first fruiting node (FFN), seed cotton yield/plant (SCY/P) and lint percentage (L %). On the other hand low heritability values in narrow sense were obtained for days to first flower (DFF), boll weight (BW), lint yield/plant (LY/P), seed index (SI), micronaire value (Mic) and Fiber elongation (Elon %). The expected genetic advance from selecting the desired 5% of F2 population was 56.098, 71.687, 29.399 and 48.12 for first fruiting node (FFN), days to first flower (DFF), lint yield/plant (LY/P) Fiber elongation (Elon %) and upper half mean length (UHM), respectively. Regression of F2/F3 results exhibited high values for first fruiting node (FFN), seed cotton yield (SCY/P), lint yield/plant (LY/P), lint percentage (L %), uniformity index (UI) and upper half mean length (UHM), indicating that the higher values due to the additive genetic variance. Positively highly significant or significant correlation coefficient was observed between days to first flower (DFF) with first fruiting node (FFN), seed cotton yield/plant (SCY/P) with boll weight (BW), lint yield/plant (LY/P) with seed cotton yield/plant (SCY/P), lint percentage (L%) with lint yield/plant (LY/P), lint index (LI) with lint percentage (L%) and Fiber strength (St), micronair value (Mic) with lint index (LI), Fiber elongation (Elon%) with Fiber strength (St) and upper half mean length (UHM) with days to first flower (DFF), lint percentage (L%) and uniformity index (UI). Negative significant or highly significant correlation coefficient were recorded between seed cotton yield/plant (SCY/P) with days to first flower (DFF), seed index (SI) with seed cotton yield/plant (SCY/P) and lint yield/plant (LY/P). It could be concluded that the selection improvement of first fruiting node (FFN), seed cotton yield (SCY/P), lint percentage (L%), seed index (SI), uniformity index (UI) and upper half mean length (UHM) traits could be achieved in early segregating generations, but the other traits need intensive selection in later generations.