The mean fitness of members of a population suffers a reduction because of deleterious mutations. Although mutation provides essential variation for selection to act upon, the vast majority of mutations reduce the fitness of the organism.

This Virtual Experiment simulates the evolution of a population of hypothetical organisms. The simulation begins with a population of identical genotypes, each encoding a value for the character under selection. Each genotype encodes the highest value possible for that character to attain: for the purposes of this experiment, we have created a hypothetical perfect population.

In each generation, genotypes are selected for breeding, and after recombination they are subject to mutation. The mutation rate determines how frequently mutation occurs: an allelic mutation rate of 0.02 means that each allele has a 1 in 50 chance of mutating. You can determine the mutation rate before running the experiment.

Once the fitness of each individual has been taken, the mutational load is calculated. Why does mutational load often seem to reach an equilibrium value? What happens to this value at different mutation rates?