Adaptive landscapes and Frequency dependent selection

The simple adaptive landscape we discussed in class shows how the mean fitness of a population (y-axis) changes with allele frequency (x-axis).

If relative fitnesses differ so: wAA = wAa > waa, then as P(A), the frequency of allele A,  increases in the population, then w-bar, the mean fitness of the population will increase and, conversely, as P(A) decreases, w-bar will decrease.

Using the adaptive landscape, you can answer questions like:

  • Will the population move towards fixation of allele A? Why?
  • Will the population move towards extinction of allele A? Why?

Note that relative fitness does not change with allele frequency.

On the other hand, if there is frequency dependent selection, then the relative fitness (w) of  a genotype (y-axis) will change with allele frequency (x-axis).

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