Mutations and Their Effects
Bad hair day? You decide.
Introduction
Look at the mouse on the right. Is there anything unusual
about it? If you said that it has no hair, then you are
correct! But how did this happen?
This hairless trait is the result of a mutation, a change in
the DNA sequence. Sometimes the change in the DNA
sequence results in a change in the recipe for the proteins
that are being produced. In this case, no hair protein!
The effects of mutations can vary widely. Some are helpful. Some are harmful. And
believe it or not, many mutations have no effect.
Stop and talk with your group to answer Question #1 on your student sheet.
Harmful Mutations
Some mutations have a negative effect on the organism in which they occur. They are
called harmful mutations. These result from random changes in a gene’s DNA that
makes proteins which do not function normally or may not function at all. For example,
imagine a population of white arctic hares that get a random mutation changing their
hair color to tan. This mutation is harmful since they no longer blend into their snowy
environment and become targets for predators. Some other harmful mutations you
may be familiar with can lead to genetic disorders or cancer. A genetic disorder is a
disease caused by a mutation in one or a few genes. One human example of a genetic
disorder is Sickle Cell Anemia, a disease in which an incorrect protein causes mis-shaped
blood cells which are unable to carry sufficient oxygen for the body. Cancer is a disease
in which cells grow out of control and form abnormal masses of cells known as tumors.
It is generally caused by mutations in genes that regulate how cells divide. The mutated
cells have damaged DNA and divide without limits. Cancer genes can be inherited,
naturally occurring, or caused by environmental factors.
Stop and talk with your group to answer Question #2 and 3 on your student sheet.
Helpful Mutations
Some DNA changes have a positive effect on the organism
in which they occur. These beneficial changes are
called helpful mutations. They lead to new versions
of proteins that help organisms adapt to changes in their
environment. For example, remember that population of
white arctic hares? Let’s view their mutation through a
different lens. Global Warming has the potential to
eliminate snow leaving some areas of bare brown ground
exposed. If the hares with the tan mutation are living in
this area, they will survive as they will blend into this new
environment. This mutation increases the hare’s chances
of surviving or reproducing, so the tan hare will become
more common over time. When considering whether a
mutation is helpful or harmful, your must take the
environment into account.
Stop and talk with your group to answer Question #4 and
5 on your student sheet.
Neutral Mutations
The majority of mutations are neutral in effect. That is they do not have either a
positive or negative effect on the organism. Neutral mutations can happen in two ways.
The first way is that sometimes mutations in coding regions are repaired before they can
cause any changes in making proteins. But, secondly, remember that not all DNA codes
for proteins. Scientist sometimes refer to these non-coding regions as “junk DNA”.
When mutations occur in these regions, there is also no change to the organism.
Stop and talk with your group to answer Questions #6 and 7 on your student sheet.
http://www.ck12.org/book/CK-12-Biology-Concepts/section/4.10/