Intraspecific hybridization among four cultivars of snapdragon, i.e. P₁ = Sonnet wit (white), P₂ = Sonnet karmijn (red), P₃ = Sonnet rose (rose) and P₄ = Sonnet geel (yellow) was carried out during three successive growing seasons: 95/1996, 96/1997 and 97/1998 at Antoniadis Botanical Garden, Horticulture Research Institute, Agriculture Research Center, Alexandria, Egypt. The main objective of this investigation was to produce new patterns of snapdragon, especially with reference to flower characteristics. Diallel cross analysis was used to study and determine the genetic system controlling vegetative growth and also the type of gene action for the different traits.  Additive and dominance gene effects were significant in the F₁ and F₂ – generations with respect to plant height. The overdominance gene effects played an important role in the inheritance of plant height. Heritability in narrow sense was intermediate in both generations and no inbreeding depression was obtained for most crosses. Most of dominant genes have positive effects and increased plant height. All F₁ – crosses achieved positive heterosis.  Additive gene effect played the major role by the inheritance of the number of branches per plant. Heritability in narrow sense was intermediate in the F₁ and F₂ generations. Most of dominant genes have negative effects and decreased the number of branches. The overdominance gene effects played an important role for F₁ hybrids and partial dominance in the F₂ generations. The dominant genes were more frequent than recessive in the parents. Most crosses achieved positive heterosis. Additive and dominance genes effects were involved in the inheritance of the number of leaves per plant. Heritability in narrow sense was moderate indicating that this trait could be advanced by selection. The degree of dominance (H₁/D)^½ was found to be overdominance in the F₁ hybrids confirmed with Wr, Vr graph. In the F₂ generations the results of Wr, Vr graph contradicted with the ratio (H₁/D)^½  indicated the presence of epistasis. Dominance genes seemed to be acted in negative direction in the F₁ hybrids and P₁ carried most recessive genes, while in the F₂ dominance genes acting in positive direction and P₂ and P₃ have most dominant genes.  In the F₁ hybrids, additive and dominance components were found to be not significant with respect to leaf area. Environmental effects were high and such large environmental role and also overdominance was involved in the inheritance of leaf area. The parent seemed to carry more dominant genes than recessive. Dominant genes seemed to be acting in positive direction and increased leaf area.