1. Mutations
Section 12-4

2. What is a mutation? Mutations are permanent changes in a cell’s DNA.
There are 2 categories of mutations:
Point mutations – involve one nucleotide
Chromosomal mutations – involve the chromosome

3. Types of Point Mutations
Substitution
One base is exchanged for another (A in place of G, for example)
Most of the time is a missense mutation, where the DNA code is altered, leading to the wrong amino acid
Occasionally it is a nonsense mutation, where a codon for an amino acid is changed to a STOP codon.

4. What happens if a Stop codon occurs in the wrong place?
When a Stop codon is reached, the ribosome stops translating…
Therefore the protein stops growing…
If the protein is not finished, it will not work properly
Will this car run
properly?

5. Is it possible to have a substitution mutation and not be aware of it?
Yes.
For example, CCU, CCC, CCA, & CCG all code for proline. If there was a substitution in the last nitrogenous base of the codon, the amino acid (and therefore the protein) would be unchanged.

6. Other types of mutations
Insertions – A nucleotide is added
Deletion – A nucleotide is removed
These are called frameshift mutations because they change the “frame” of the amino acid sequence.
Duplications and expanding mutations involve repeated codons.

7. Results of Mutations
Most of these mutations result in genetic disorders.
Why?
The order of amino acids relates to the way the protein folds & to its stability.
The way the protein folds relates to the protein’s function.
Diseases caused by incorrect protein folding include sickle cell disease, Alzheimer’s disease, cystic fibrosis, diabetes, and cancer.

8. What causes mutations? Some mutations occur spontaneously.
Others are caused by mutagens, which can alter the chemical structure of the bases and allows them to pair incorrectly.
Examples of mutagens are X rays, UV radiation, etc.

9. Body cell vs. Sex cell mutations
Body cells are not passed on to offspring, so mutations in your body cells affect YOU, but not your children.
Mutations in the sex cells are passed on to your CHILDREN because they start out as one cell that contains the mutated DNA.

10. Is it possible for mutations to be good?
Yes.
Mutations increase genetic variation.
Sometimes mutations provide something beneficial (more dense bones, for example)
This is how evolution starts.