Download 4.2 Mutation

BC Science 9:
p. 136-147
Gene Mutation
A gene mutation involves a change in the order of
the bases (A, C, G, T) that make up the gene.
 There are three types of gene mutations:

 Deletion (base missing)
○ AGTCTGC  AGCTGC
 Addition (extra base added)
○ AGTCTGC  AGTCGTGC
 Substitution (one base is substituted for another)
○ AGTCTGC  AGGCTGC
The Effect of a Gene Mutation
Gene mutations may cause an organism to produce
proteins that are beneficial or harmful to it, or may
have no effect at all.
 The effect of the gene mutation can be positive,
negative, or neutral.

Positive Gene Mutations

When a gene mutation benefits the individual.
 Eg. Some plants have developed resistance to bacterial and
fungal infections. These plants are able to produce
proteins that protect them.
Negative Gene Mutations

When a gene mutation harms the individual.
 Eg. Red blood cells are unable to create the protein
hemoglobin and take on a different shape. These abnormally
shaped cells cannot carry oxygen efficiently and cause sickle
cell anemia and organ damage.
Neutral Gene Mutations
When a gene mutation has no effect on the individual.
 The most common of the three types.

 Eg. A mutation in the DNA of the white Kermode bear
causes its fur to be white instead of black. Studies have
shown that the fur colour has no effect on the bear’s
survival.
Mutagens

Substances or factors that cause mutations in DNA are
known as mutagens.
 Eg. Cigarette smoke, radiation from UV rays or X-rays,
pollutants such as mercury or cadmium, certain viruses, or
household chemicals.
Mutagens
Mutagens change the
sequence of bases and cause
the DNA to become
damaged.
 The damaged DNA can
disrupt the instructions
stored in genes and inhibit
the correct proteins from
being produced.

Correcting Mutations
Correcting mutations is difficult, but new
techniques such as gene therapy offer hope.
 Gene therapy is complicated, expensive and
experimental.

Gene Therapy
A virus is engineered to carry a normal gene.
2. The virus must target the cells with the defective
gene.
3. The normal gene must replace the defective gene.
4. The normal gene must then be “switched on” so that
the replaced gene produces the proper healthy
protein.
1.