Heritability - Equations

There are three ways to calculate narrow sense heritability:

Using mean trait values...
Heritability can also be thought of as the portion of selection in the parent generation that shows up in the offspring. This can be calculated using the response to selection, R, and the selection differential, S, as follows:

Using variance components...
From its definition, we can calculate narrow-sense heritability as:

Total Phenotypic Variation Vp = Vg + Ve
Variation Due to Genes Vg =  Va + Vd + Vi
Variation Due to Additive Effects of Genes Va
Variation Due to Dominance Effects Vd
Variation Due to Epistasis/Interaction Vi
Variation Due to the Environment Ve

Using a parent-offspring regression...
Determining the functional relationship between mid-parent trait values and corresponding offspring values also yields a method of measuring heritability. In particular, the slope of the best-fit regression line is the heritability of that trait. This can be calculated using the equation for the regression coefficient: