If you do not see an applet here, chances are that you are using Netscape with Mac OS. Not to worry you are only 8 clicks away from viewing this applet.

1. Please download the Apple Runtime for Java available for FREE at (if you already have the Apple Applet Viewer, skip to step 5):


2. Once the program has downloaded, click on the the MRJ2.2.2.smi icon on your desktop.

3. Click on the MRJ Install icon to install the applet viewer.

4. Open the Apple Applet Runner Folder

5. Click on the Apple Applet Runner Icon

6. In the file menu select Open location

5. Copy the URL of this page and paste it into the Location box of the Applet Runner window.

6. Click Open. The applet may take a moment or two to load.

It will be worth your time, I promise!

NOTE: You can also save the applet in your Apple Applet Viewer Favorites if you want to access it more quickly next time. Do the following:

When the applet is loaded, go to the applets menu and select add applet to list.

Natural Selection: Estimating Heritability

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:

Natural Selection: Estimating Heritability

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