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Narrow sense heritability is the proportion of total phenotypic variation that is due to the additive effects of genes. This component of variation is important because it is the only variation that natural selection can act on. Broad sense heritability is the proportion of total phenotypic variation due to all genetic effects.

**There are three ways to calculate narrow sense heritability:**

From its definition, we can calculate narrow-sense heritability as:

**Adjust the variance components to the right:**

**Total Phenotypic Variation Vp** = Vg + Ve

**Variation Due to Genes Vg** = Va + Vd + Vi

**Variation Due to Additive Effects of Genes Vg**

**Variation Due to Dominance Effects Vd**

**Variation Due to Epistasis/Interaction Vi**

**Variation Due to the Environment Ve**

Determining the functional relationship between mid-parent trait values and corresponding offspring values also yeilds a method of measuring heritability. In particular, the slope of the best-fit regression line is the heritability of that trait.

**Adjust the slope of the best-fit regression line to the right:**

Scroll over a method above for more information about...

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:

**Adjust R and S to the right:**

**Choose a method for estimating heritability. Then adjust the parameters to determine the effect on the heritability estimate:**