Gene mutations occur when the sequence of nitrogen bases that make up a gene changes. There are three types of mutations: substitutions replace one base with another, additions insert an extra base, and deletions remove a base. Mutations can have positive, negative, or neutral effects on an organism's chances of survival. Mutagens like viruses, smoke, radiation, and chemicals cause DNA mutations and sometimes lead to cancer. Gene therapy aims to correct mutations by replacing the mutated gene with a healthy copy delivered via inactive viruses, though it remains experimental.

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

12. Gene Therapy

13. Inherited Traits