Forty-five intra-and interspecific diploid or desi cotton hybrids (G. arboreum x G. herbaceum) derived from half diallel mating design, by involving ten diverse parents of G. herbaceum and G. arboreum were evaluated to study combining ability for seed cotton yield and its component traits. Mean squares due to GCA and SCA variance were highly significant for all the 11 agro-morphological characters studied. The variance due to GCA and SCA for mean squares was highly significant, which suggested that additive and non-additive gene action is involved for controlling all the characters. Combining ability analysis suggested the preponderance of non-additive type of gene action for all the traits except days to 50% flowering and no. of monopodia per plant. Based on per se performance, parent GAM-165 and cross GBhv-282 x G27 was superior for seed cotton yield and lint yield per plant. The parent G-27 and GBhv-287 was found to be the best general combiner for majority of the traits. Based on sca effects, GBhv-282 x G 27 exhibited significant sca effects for seed cotton yield per plant, lint yield per plant, number of bolls per plant, boll weight and no. of sympodia per plant. Heterosis breeding will be useful for diploid cotton improvement due to presence of non-additive type of gene action.

A wide array of sex determination mechanisms, encompassing genetic and non-genetic pathways (i.e., hormonal, environmental, and epigenetic factors), have been found among different organisms. The presence of two complementary sexes, male and female, is an ancient feature in biology. Triggering the differentiation of male and female reproductive organs is a conserved ontogenic process, and sex determination is an inherently fascinating process. Sex determination is dependent on molecular signaling whether the male and the female differentiating pathway is activated, and different triggering elements such as genetic, non-genetic, and epigenetic factors control the whole process. This chapter describes various aspects of sex determination, such as historical development, the evolution of sex chromosomes, and different sex determination systems in other organisms.

The present investigation was carried out to assess the expression of per se performance and heterotic effect for fibre quality and seed oil content besides seed cotton yield, studied involving ten desi cotton (Gossipium arboreum and G. herbaceaum) genotypes and their 45 cross combinations in half diallel analysis. F-1 hybrids GBhv- 282 x G 27 (67.36%), GBhv- 287 x 824 (58.14%), GBhv- 282 x GAM- 173 (35.00%), GBhv- 286 x G 27 (20.50%), and GBhv- 283 x 824 (18.75%) recorded highest per se performance and significant positive standard heterosis while the maximum heterobeltiosis for seed cotton yield per plant was exhibited by the hybrid GBhv- 287 x 824 (155.60 %) followed by GBhv- 282 x G 27 (151.29%) and GBhv- 282 x GAM- 173 (130.30%). Similar trend of heterosis for numbers of boll per plant were observed in above hybrids. For fibre quality traits none of the cross showed consistent high performance for all the characters. Cross GBhv- 283 x 824 was exhibited high standard heterosis for 2.5 % span length, fibre strength, fibre elongation percentage as well as for short fibre index (SFI) while cross GBhv- 286 x 824 were promising for 2.5 per cent span length, fibre strength and fibre fineness. In case of oil content intraarboreum crosses resulted as better crosses and among them cross combination 824 x GAM- 173 was best. Desi cotton hybrids are having lower fibre quality and yield. So, improvement for yield and fibre quality of diploid native varieties through heterosis breeding provided better hybrids for rainfed farming.