Pakistan ranks at 4th position with respect to global area and production of cotton, however the yield level is still low as compared to other major cotton producing countries. There are so many pathways which contribute to the final yield of cotton plant, one of which may be the exploitation and selection for some basic traits related to boll. Keeping in view the importance of within-boll yield components in determining the final yield, present study was carried out in research area of the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad to estimate the genetic basis of various yield and quality attributes, combining ability and heterotic manifestation and correlation of agronomic, boll related and fibre quality traits in Gossypium hirsutum L. For this study two crosses were made involving four contrasting parents with respect to seed cotton yield and fibre quality characters. Crosses were made following triple test cross model and data on various agronomic, boll related and fibre quality traits were recorded and analyzed. Significant amount of epistatic interaction was found to be involved in expression of almost all the traits. The additive variance was greater in magnitude that dominance variance for traits like number of bolls per plant, seed cotton yield per plant, lint percentage, lint index, fibre fineness, lint mass per boll and lint mass per seed resulting in partial degree of dominance for these traits. While dominance variance was found to be greater in magnitude than additive variance for average boll weight, fibre length, fibre strength, number of seeds per boll, seed mass per boll, seed index, seed volume and seed surface area resulting in over-dominance type of gene action. Seed density showed complete dominance of the genes. BH-89 showed highest positive GCA effects for most of the traits. Among testers, CIM-1100, CIM-496and FH- 634 showed significant GCA effects for most of the traits. NIAB-999 × CIM-70 proved to be the best regarding seed cotton yield per plant and seed surface area. Combination of S- 12 with (NIAB-228 × BH-160) showed maximum value regarding lint percentage, fibre length, seed volume and seed surface area, it also proved to be the best for seed density when combined with NIAB-228. The highest value of mid and better parent heterosis regarding number of bolls per plant (43.60% and 25.52%), seed cotton yield per plant (61.41% and 30.67%) and seed number per boll (17.28% and 16.14%) was observed for the hybrid BH-89 × CIM-496. Correlation studies revealed that bolls per plant were positively associated with seed cotton yield. Average boll weight showed significant positive correlation fibre strength and seed cotton yield. In the second cross, number of bolls per plant showed positive correlation with boll weight, fibre strength and seed cotton yield. Number of seeds per boll was positively associated with lint percentage, fibre length and seed cotton yield. Fibre length and fibre fineness were negatively correlated. Fibre length showed positive association with seed cotton yield.