Few crosses also involved two best general combiners (e.g., Danilla x IT97K-499_35); this indicated the importance of additive and additive x additive gene action
in the inheritance of these traits and also indicated rapid genetic progress in advanced generations under water stress.
This could be explained from the point of view of gene action since gca is mostly due to additive gene action
whereas sea is mostly due to overdominance and epistasis.
followed by Mather and Jinks approach and confirmed the role of additive gene action
. Whereas Zhang et al.
Additive gene action
is effectively responsive to selection whereas, non-additive gene action (dominance and epistatic) enhances the hybrid vigor in cross combination of inbred lines.
Significant additive gene action
was found in all populations in the genetic study, suggesting that later family selection for resistance should be more efficient.
Graphical representation displayed additive gene action
with partial dominance for tillers per plant, grain yield per plant, 1000-grain weight and plant height and over dominance for flag leaf area.
With additive gene action
, standard plant-breeding procedures, especially recurrent selection, would be useful to improve both groat protein and oil content (Campbell and Frey, 1972).
Although, additive gene action
is there but presence of additive x dominant (j) epistasis made the gene action complex leading towards a delay in selection.
Changes in genetic variances within and among subpopulations at low values of [F.sub.ST] (i.e., at the beginning of population subdivision) are affected by dominant gene action in two ways: (i) total genetic variance and additive variance within subpopulations are increasing at low values of [F.sub.ST], whereas they decrease linearly in [F.sub.ST] with additive gene action
; and (ii) variance among subpopulations increases much more slowly than expected under an additive genetic model (Robertson, 1952; Willis and Orr, 1993; Wang et al., 1998).
A diallel analysis of eight tobacco accessions demonstrated that general combining ability (GCA) effects accounted for the majority of variation observed among crosses (Hayes et al., 1995) and suggested that additive gene action
plays a significant role in the inheritance of resistance to G.
GCA/SCA ratio was more than unity for 100-seed weight showing the preponderance of additive gene action
. Heterosis breeding for the improvement of all traits while, recombination breeding for 100-seed weight were suggested.
Under the assumptions of large population size (and thus no drift during selection), additive gene action
, equal allelic effects among loci, and initial allele frequencies of 0.5, this ratio is eight times the number of loci affecting the selected trait, and forms the basis for the Castle-Wright estimator of that number (Falconer and Mackay, 1996; Lynch and Walsh, 1998).