Transcript Gene Mutations - Valhalla High School

Gene Mutations
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Changes to the
nucleotide sequence of
the genetic material of
an organism.
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Dr. Timmel
Mutations
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Mutations arise when the sequence of
nucleotides within an organisms nucleic acids is
changed.
The impact of these mutations on the organism
can range from life threatening to completely
inconsequential.
Mutations are random, though some risky
behaviors can put an individual at a greater
danger of a mutation.
The good, the bad and the ugly.
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Mutations are an important
ingredient to the theory of
evolution by natural selection, as
they increase the amount of
genetic diversity in a population.
Usually (>99%) mutations are
deleterious (bad) to an organism.
However, on occasion, a mutation
gives an individual a selective
advantage, and will increase in
frequency within a population.
Mutations will never, ever give you
superpowers.
What causes mutations?
Agents that can cause
mutations are called
MUTAGENS.
Some examples are:
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1.
2.
3.
Chemicals (Such as the
ones in cigarette smoke)
Ultra-violet or ionizing
radiation
Viruses
Types of genetic mutations.
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There are two main categories of mutation.
Point mutations and frame shift mutations.
In a point mutation, a single nitrogen base is substituted with
another.
e.g. Normal gene =ATA CCG GCA TTA
Mutated gene =ATA CCG TCA TTA
In this example, a guanine base has been substituted with a
thymine.
Outcomes of point mutations
There are three
possible outcomes of a
point mutation.
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1.
Silent mutation: The
mutated codon codes
for the same amino
acid. The protein will
be unchanged.
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For instance, if the
codon AAA is mutated
to AAG there will be no
difference in the the
protein that is translated.
That is because both
AAA and AAG code for
the same amino acid.
Point mutations cont.
2. Small change mutation(missense mutation): A
single amino acid in a protein will be different.
The protein will function, but not as well as an
unmutated one. Sickle-cell anemia is the result
of this type of point mutation
 In this disease, a codon which normally would
code for Valine is mutated into one that codes
for Glutamic Acid.
Point mutations (cont.)
3. The stop command mutation (nonsense
mutations): The mutation causes a codon that
would have coded for an amino acid to instead
code for the stop command. This will lead to
incomplete protein fragments that will not
function.
Types of genetic mutation (cont.)
2. Frame shift mutations: A nitrogen base is
either added (insertion) or removed (deleted)
from a gene.
Normal gene: ATA CGG CTA TTC
Insertion:
ATA CGA GCT ATT C
Deletion:
ATA CGC TAT TC
(a guanine was deleted)
Results of a frame shift mutation
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Except in the case of the stop command point
mutation, frame shift mutations are much worse
than point mutations.
In a gene that has been afflicted with a frame
shift mutation, it is unaffected prior to the
location of the mutation, but then completely
garbled afterwards.
Lets look at an analogy to help illustrate this.
Frame shift analogy
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Consider the following sentence:
“The fat cat sat and ate rat”.
This represents the normal gene. Each 3-letter
word represents a codon in the gene.
Now let us consider what happens in an
insertion mutation. Lets insert a “a” between
the t in “cat” and the s in “sat”.
The gene would now look like this
Insertion cont.
The fat cat asa tan dat era t
As you can see, the portion of the gene before
the insertion is unchanged, but from the
location of the insertion onwards, the gene is
now nonsense.
This gene will not translate into a useable protein.
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Deletion
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A deletion also causes a frameshift, and just like
in an insertion, everything from that point will
be altered.
Let’s delete the S from sat in our example.
Now it looks like this.
The cat ata nda atr at
Can mutations be passed on to your
children?
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Yes, but only if the occur in the sperm or egg
cells.
These types of cells are referred to as sex cells,
or germ cells.
Mutations that occur in your body cells, which
are also known as somatic cells, are not passed
on to your children.