Heritability I

This Applet demonstrates the relationship between genotypic values and phenotypic values for different heritabilities. Enter a value for the heritability, a value for the number of observations and then click the Submit button. The Applet will plot a scatterplot of genotypic and phenotypic values for the heritability.

Exercises:

  1. Set the heritability to 0.0 and the number of observations to 1,000. Click the Submit button several times, pausing between each click to let the program "paint" a number of dots on the screen. Every time that you click Submit, the program will generate 1,000 random observations and for each observation, plot a point for the genotypic value and phenotypic value of the observation.
    Notice how the points in the scatterplot form a rough circle. This implies a total lack of predictability--if you know a person's genotypic value, it is not possible to predict that person's phenotypic value with any degree of accuracy.
  2. Set the heritability to 1.0 and the number of observations to 50. In this case, all the points fall on a straight line. This demonstrates perfect predictability--if you know a person's genotypic value, then you could perfectly predict the person's phenotypic value.
  3. Intermediate values of heritability produce scatterplots that resemble an ellipse. With low heritabilities (.10, .20), the ellipse approaches a circle, and with higher values (.80, .90), the ellipse approaches the straight line. To verify this, reset the number of observations to 1,000 and then enter some low values and then some high values of heritability.
  4. The heritability for most behavioral traits is in the intermediate range (say, .30 to .60). Enter some intermediate values. This will give you some indication of the extent to which genetic individual differences contribute to individual differences in actual, observed behavior. Note how individuals with the same (or very similar) genetic values have a range of phenotypic values. To get a full appreciation of this, set the number of observations to its maximum value of 10,000, click Submit, and then imagine a vertical line drawn at a genotypic value (i.e., a line perpendicular to the horizontal axis). All the points that touch the line have virtually the same genotypic value, but they can differ quite a bit on their phenotypic values.

Links:

Heritability: Introduction
Heritability II: Environmental variation around a genotypic value.
Heritability III: Culture and heritability.
Heritability IV: Between-group Heritability.