First we need to calculate within and between family variance components for half sib families. Additive variance is equal to 4 time the additive variance and Dominance variance equal to within family variance - (3/4) additive variance.

No. Variance is always positive and so the sum of variances must also be positive.

Heritability

Heritability

Broad sense heritability A.K.A (H) is the degree in which phenotypic variation is due to genetic factors

Narrow sense heritability A.K.A (h) is the degree in which phenotypic variation is due to additive genetic factors.

in maths terms...

H = Vg/Vt

h = Va/Vt

Vg= genetic varaition

Vt = total variation

Va = additive variation