Genetic Variability, Random Mutation & Artificial Selection

Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

In this lesson we will discuss the importance of genetic variability and the role of random mutations. We will also compare the processes of natural and artificial selection.

Importance of Genetic Variation

The theory of evolution is the idea that species on Earth today evolved from species that previously existed. The idea is that, over long periods of time, new traits that benefit a population replace traits that are less useful and species change. However, this doesn't mean that an individual organism can change of its own accord. Instead, a population of organisms will express traits in more than one way. These naturally occurring differences are called genetic variation.

Genetic variation can be seen in any population. Let's imagine a population of beetles. All of the beetles may be similar looking, but perhaps they vary in color or pattern. Some are brownish while others appear greenish. A few may even be orange or yellow.

When you think of a ladybug you probably imagine a red bug with black spots. But they actually exist in a variety of different colors such as the yellow and black ladybugs pictured here.

Genetic variation is essential for a species' capacity for change. When an outside force impacts a population, genetic variation provides a choice of traits to select from. Changes to the environment are the most common outside force to act upon a species in nature. In natural selection, the traits that are most suited for the environment are passed on to future species. If the environment changes, organisms with new, more beneficial traits are 'selected', or in other words are more likely to reproduce.

Genetic Variability

Now that we understand that genetic variation is the naturally occurring differences in a population, let's take a look at genetic variability. These terms sound the same, but there is a key difference. Genetic variability is a measure of how much a trait varies within a population. The greater the degree of variation in a particular trait, or the greater the genetic variability, the greater a population's ability to adapt to changes in the environment. Less genetic variability, or less variation in a trait, makes it less likely a population will be able to adapt.

Let's think about our population of beetles again for a moment. It is beneficial for the beetles to blend in with their environment. Having a wider variety of colors in the population can help ensure this is possible even if the color of the plants they live on changes. The more colors of beetles in the population, the better able they are to adapt to different colors of plants. Say for example that you have a population of beetles, most of which are green but some of which are yellow. This works because most of the plants in their environment are green as well. What do you think would happen if the majority of plants in the environment become yellow? The yellow beetles would blend in better than the green ones and be more likely to survive. Over time, the population of beetles would be mostly yellow instead of green.

Our beetle example demonstrates how a population needs enough genetic variability to be able to survive and adapt to environmental changes. What might have happened if only green beetles existed within the population? When the plant color became yellow, the green beetles would have been easy for predators to find. The inability to adapt to the new color of plants could have resulted in the extinction of the population.

Each different color of beetle provides the potential for the population to adapt to that corresponding color of plant. Two different beetle colors in the population provides an opportunity to adapt to two different colors of plants. Five different beetle colors provides the possibility to adapt to five different plant colors. And ten different beetle colors provides the potential to adapt to ten different colors of plants.

Random Mutation

Where does genetic variability come from? Some genetic variation will be naturally inherited as offspring are produced. However, the greatest amount genetic variability occurs through random mutation. Random mutations are random changes that occur in DNA when it does not replicate properly. When there is a change to the DNA, traits can be significantly altered. If this alteration results in a harmful trait, it will usually be eliminated from the population quickly and will not be passed on to very many future generations. However, if the mutation is beneficial it is more likely to be passed on and may eventually be incorporated into the entire population.

A good example of this is antibiotic resistant bacteria. Imagine that you have a bacterial infection. You take an antibiotic and most of the bacteria die. However, a few of the bacteria have a random mutation that makes them resistant and therefore able to survive exposure to the antibiotic. They reproduce and you are re-infected with only antibiotic resistant bacteria. This random mutation is good for the survival of the bacteria, but bad for you!

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