Evolutionary Biology at The Biology Project

Simulation of Mutation plus Drift

Mutations in a Population

Mutations are the ultimate source of all genetic variation.

Mutations produce new versions of genes (new alleles). When new alleles appear, the genetic variation in a population increases.

mutations    new alleles    more genetic variation

How often do mutations occur?   The mutation rate

The mutation rate is the number of mutations per genetic unit (gene, base, or product) per unit time (year, million years, or generation). This is how to calculate the mutation rate:

Calculate mutation rate

Consider the worm population below. The population size (N) is 3. Each worm has a complete gene sequence that is 10 bases long. Only new mutations are flagged with an M.

Generation 1 Generation 2 Generation 3

What is the mutation rate per gene per generation? What is the rate per base per generation? How many mutations can you expect an average worm to carry?

Here are some mutation rates for your favorite organisms.
[table here]
Notice that different units are used to express the mutation rate in different organisms.

Notice that mutations are very rare. Mutation rates are very low for most organisms. Think about it, you might look at three million gametes and only find ten mutants.

On the other hand, mutation happens. [calculations still needed here] insert calculations here
We are all mutants. Fortunately many have little or no effect.

Mutation Drift Balance

In the Genetic Drift Simulation, the number of color alleles in the population (genetic variation) decreased due to genetic drift (eventually to only one allele). 

In this simulation, mutation adds alleles and increases genetic variation while drift removes alleles and decreases variation.

These two forces can balance each other.

<< About Mutation| About the Mutation-Drift simulation >>

Mutation [Evolution] [Vocabulary] [The Biology Project]

The Biology Project
The University of Arizona
April 27, 1999
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