Heritability IV

This Applet plots the phenotypic distributions for two different cultures so that you can easily compare them. The exercise serves two purposes. First, it may help you to answer the problem given in Heritability III. Second, it introduces the concept of between group heritability. If you are doing this to gain insight into the Heritability III problem, then simply ignore the issues of between group heritability for the moment. You can pick up on the topic by redoing the exercises given below.

The heritability that we have been dealing with thus far may be termed within group heritability because it pertains to individual differences within a population. Between group heritability pertains to differences between populations and as you might imagine, it is an index of the extent to which genes contribute to the differences in population means. Between group heritability will be 0 when the populations have the same allele frequencies for the genes that contribute to the trait. However, the converse of this statement is not true. If the populations have different allele frequencies, then the between group heritability does not have to be greater than 0. The reason is simple. Population 1 may have a higher frequency than population 2 for the favorable allele at the A locus, but population 2 may have a higher frequency of the favorable allele at the B locus-the effects of the differing allele frequencies cancel out and there is no (or very little) between group heritability.

Your task in this lesson is to give numerical values for two different culture, the "red" culture and the "blue" culture. The program will plot the distributions for each culture and print the within group heritabilities. At the very top of the plot, an estimate of the between group heritability will be printed.

Exercises:

  1. Think of two very different cultures and enter the respective values for the traits for each culture. Examine the two curves and write down the two within group heritabilities and the between group heritability. Do not worry if the between group heritability equals "??." This means that the between group heritability cannot be calculated from the numbers that you entered.
  2. Repeat exercise 1 for two cultures that are only slightly different from each other-say by only 10 points on each of the traits. Again, write down the within and between group heritabilities.
  3. Repeat exercises 1 and 2 several times and keep examining the within and between group heritabilities. If you keep getting the same answer for the between group heritability, don't cuss the program because you think it is messed up and don't think that you are not correctly following the instructions. The results may be telling you something very, very important about how within group heritabilities relate to between group heritabilities. What do you think it is?

Links:

Heritability: Introduction
Heritability I: Scatterplots
Heritability II: Environmental variation around a genotypic value.
Heritability III: Culture and heritability.