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

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

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.

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

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.

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.

Effects of Mutation

POSITIVE

◦ Increases an organisms chance of

survival

◦ Very rare

◦ Ex. Scientists have discovered a mutation

that makes individuals resistant to HIV

Effects of Mutation

NEGATIVE

◦ Decreases an organisms chance of

survival

◦ Ex. Cystic Fibrosis and Sickle Cell Anemia

Effects of Mutation

NEUTRAL

◦ Does not affect an organisms chances of

survival

◦ Most Common

◦ Ex. White fur of the

Kermode (Spirit) Bear

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)

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

Gene Therapy

Inherited Traits