Genetic (co)variance components (1) [[sigma].sup.2.sub.a] c [[sigma].sup.2.sub.e] Birth 0.004 [+ or -] 0.016 0.164 [+ or -] 0.247 [+ or -] 0.02 weight 0.024 Genetic parameters (2) [h.sup.2.sub.a] [c.sup.2] [e.sup.2] Birth weight 0.011 [+ or -] 0.04 0.394 [+ or -] 0.595 [+ or -] 0.053 0.045 [[sigma].sup.2.sub.p] Birth 0.416 [+ or -] 0.025 weight Birth weight (1) [[sigma].sup.2.sub.a]: Direct
additive genetic variance; c: Variance attributed to the permanent maternal environment; Residual variance; [[sigma].sup.2.sub.e]: Phenotypic variance.
The estimates of
additive genetic variance and heritability from this study are not precise because of the small numbers of families and parents in this trial.
This is because most of the genetic variance expressed by structural genes is additive and because genes with epistatic effects influence the response to individual selection through their contribution to the
additive genetic variance (Crow and Kimura 1970).
The models, explaining within a between variances (Table 3) on the basis of two genetic components and two environmental components, viz.,
additive genetic variance (DR), dominance (HR), within family environment ([E.sub.1]), and between family environment ([E.sub.2]) were applied to data on twins reared together having nonsignificant G x E interaction (Table 4).
The estimated
additive genetic variance for development time was higher in females than in males (Table 2).
Additive genetic variance had increasing trend during the lactation trajectory.
In this study, the direct
additive genetic variance for milk yield represents 44.9% from phenotypic variance while the maternal genetic variance and the maternal permanent environmental variance are 22.1% and 4.4%, respectively.
where A is the Wright's additive relationship matrix [60] among all animals in the pedigree, [[sigma].sup.2.sub.a] is the direct
additive genetic variance, [[sigma].sup.2.sub.m] is the maternal
additive genetic variance, [[sigma].sup.2.sub.c] is the maternal permanent environmental variance, [[sigma].sup.2.sub.e] is the residual variance and [I.sub.c] and [I.sub.n] are identity matrices of size equal to the number of dams and the number of observations, respectively.
It was estimated the heritability coefficient at average level ([h.sup.2.sub.m]), the
additive genetic variance for half-sib progenies, which corresponds with 4[[sigma].sup.2.sup.p], and variation index b that is estimated by the relation between the genetic variation coefficient and environment variation coefficient (CRUZ et al., 2003).
Epistasis as a source of increased
additive genetic variance as population bottlenecks.
The phenotypic variance ([V.sub.P]) was separated into the
additive genetic variance ([V.sub.A]), non-additive genetic variance ([V.sub.N] and environmental variance ([V.sub.E]), and the environmental variance ([V.sub.E]) was separated into the common environmental variance ([V.sub.E]) and the specific environmental variance ([V.sub.ES) using the standard separation of variance components (Falconer 1989).
The square root of direct (i.e., Mendelian) heritability ([h.sub.o]), path coefficient 1, represents the square root of the fraction of the total phenotypic variance in the trait of interest [Mathematical Expression Omitted] that is determined by the direct
additive genetic variance [Mathematical Expression Omitted], whereas the path coefficient 2 represents the proportion accounted for by random environmental variance ([Mathematical Expression Omitted]).
