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Six divergent cotton genotypes were crossed in un-constructed to be 15 F1 crosses then, F2 were obtained. All genotypes were evaluated in Randomized Complete Block Design with three replicates. Genetic parameters of natural performance of genes were estimated by Hayman method (1954) for characters of Boll weight (B.W.), Seed cotton yield (S.C.Y.), Lint yield (L.Y.), Seed index (S.I.), Lint percentage (L. %), Lint index (L.I.) and oil%. The result showed that additive and dominance variance H1 and H2 values were significant for all traits, and the additive values were less from dominant values, that refers to the importance of dominance variance in its inheritance. Also, the H2 values were less than H1 which recorded that the allelic frequencies were not equal. The overall dominance effects of heterozygous loci (h² ) were significant for all traits in both generations, indicating that the dominance was due to heterozygosity and was unidirectional with appreciable heterotic effect. The proportion of dominant to recessive gene in parents KD/KR were more than unity for most studied traits. The average degree of dominance (H1/D)0.5 exceeded unity for all studied traits in both generations, indicating that presence of over dominance for these traits. High values for heritability in broad sense were obtained for all traits, revealing that most phenotypic variability in each trait was due to genetic causes. High heritability values in broad sense along with medium or low ones in narrow sense were exhibited in both generations, indicating that most genetic variances were due to non-additive genetic effects. The regression line passed through the origin in boll weight in generations, seed index, lint percentage and oil% in F1, revealed a presence of complete dominance. Meanwhile, it intersects the Wr axis above the origin in lint yield and oil% in F2, reflecting partial dominance. The P4, p2, P2, P5, P5, P2 and P5 in F1, P4, P2, P1, P5, P6, P3 and P6 in F2 for B.W., S.C.Y., L.Y., S.I., L. %, L.I and oil%, respectively seemed to have the highest number of dominant genes. [ABSTRACT FROM AUTHOR]

Heterosis and gene action on oil%, and yield traits were determined in a 6x6 diallel cross of cotton without reciprocals and their F2 generation to define and select an efficient and prospective material for immediate use in hybridization programs to improve seed yield of cotton in Egypt. Parents, F1 and F2 were evaluated in a randomized complete block design (RCBD) with three replicates for yield traits in 2021 season. High significant mean squares for genotype, parents and crosses were showed for the studied traits in both generations. Significant heterosis in F1 generation was obtained for all studied traits. The desirable heterosis of relative to better parent varied from 5.36 to 25.29, 5.92 to 33, 2.3 to 5.89 and 1.14 to 7.38 in F1 generation for seed cotton yield, lint yield, seed index and oil%, respectively. The cross P2xP3 was the best cross for all studied traits heterosis. Mean squares for general (GCA) and specific (SCA) combining ability were significant for all studied traits. MS (GCA)/ MS (SCA) ratios displays the relative importance of additive and additive by additive gene action effects in their inheritance for seed cotton yield, lint yield, seed index and lint percentage in F1 generation and seed cotton yield and lint yield in F2 generation. P1 exhibited significant desirable ĝi effect among all the tested parents for lint percentage, lint index and oil% in F1 and seed cotton yield, lint yield and oil % in F2. The cross P2xP3 showed significantly desirable SCA effects for most studied traits. [ABSTRACT FROM AUTHOR]