1. 4d: Gene Mutations
• Define gene mutation
• Identify and describe the 3 different types of
gene mutations and how severe their effects
are
• Describe the 3 different effects of gene
mutations
• Define and provide examples of mutagens
• Explain the purpose of gene therapy
2. Gene Mutations
A gene mutation results when the
specific sequence of A,G,C & T bases
that make up a particular gene
changes
Gene mutations can occur at any time
during the life of a cell
3. Reading the Code
The DNA code – arrangement of
nitrogen bases (A,T,C,G) is read in
groups of three called codons
Each codon gives the instruction for a
specific amino acid to be added to a
protein.
4. 3 Types of Gene Mutations
SUBSTITUTION:
◦ One nitrogen base is replaced with another
base
SAM MET BAT MAN
SAM MET CAT MAN
◦ Only one codon is affected. New gene may
still make sense
5. 3 Types of Gene Mutations
ADDITION
◦ An extra nitrogen base is inserted into the
DNA code
SAM MET BAT MAN
SAM MEL TBA TMA N
◦ All bases following insertion are affected.
New gene likely no longer makes sense.
6. 3 Types of Gene Mutations
DELETION
◦ A nitrogen base is deleted from the DNA
code
SAM MET BAT MAN
SAM ME B ATM A
◦ All bases following deletion are affected.
New gene likely no longer makes sense.
7. Effects of Mutation
POSITIVE
◦ Increases an organisms chance of
survival
◦ Very rare
◦ Ex. Scientists have discovered a mutation
that makes individuals resistant to HIV
8. Effects of Mutation
NEGATIVE
◦ Decreases an organisms chance of
survival
◦ Ex. Cystic Fibrosis and Sickle Cell Anemia
9. Effects of Mutation
NEUTRAL
◦ Does not affect an organisms chances of
survival
◦ Most Common
◦ Ex. White fur of the
Kermode (Spirit) Bear
10. Causes of Mutations
Substances or factors that can cause
DNA to mutate are called mutagens
◦ Viruses
◦ Cigarette smoke
◦ Radiation (X-rays, UV rays)
◦ Pollutants
◦ Chemicals
DNA mutations can sometimes lead to
cancer so mutagens are sometimes also
called carcinogens
(more about cancer in Ch 5)
11. Correcting Mutations
Gene Therapy
◦ Cells affected by the mutation are
targeted and the mutated gene is
replaced by a copy of the DNA with a
healthy gene
◦ Healthy genes are often delivered to
target cells via inactive viruses
◦ Gene therapy is currently experimental
and can be risky
◦ http://youtu.be/bLI1Gfb0ynw
