8.7 Mutations

KEY CONCEPT Mutations are changes in DNA that may or may not affect observable traits/characteristics.

8.7 Mutations

Some mutations affect a single gene, while others affect an entire chromosome.

• A mutation is a change in an organism’s DNA.• Many kinds of mutations can occur, especially during

replication.• A point mutation substitutes one nucleotide for another.

mutatedbase

8.7 Mutations

• Many kinds of mutations can occur, especially during replication.

– A frameshift mutation inserts or deletes a nucleotide in the DNA sequence.

8.7 Mutations

Mutations may or may not affect observable traits.

– A mutation may cause a premature stop codon.– A mutation may change protein shape or the active site.

blockage

no blockage

The coronary artery supplies blood to the heart. A mutation exists that protects against blockages.

Cystic Fibrosis is caused by a deletion.

8.7 Mutations

• Some gene mutations do not affect observable traits.

– A mutation may be silent.– Many amino acids have more than one code

– Ex: AAG and AAA are both lysine– A mutation may occur in a noncoding region.– A mutation may not affect protein folding or the active

site.– Changed amino acid may have the same size and

polarity and may not change the function much

8.7 Mutations

• Mutations in body cells do not affect offspring. These cells are not passed on to offspring.

• Mutations in sex cells are passed on and can be harmful or beneficial to offspring.• Usually, offspring do not develop properly and are not

able to reproduce• Natural selection often removes mutant genes from a

population when they are less adaptive.• Rarely, a mutation results in a superior trait that is

passed on and causes an increase in population.

Impact on Offspring

8.7 Mutations

Mutations can be caused by several factors.

**Mutations can happen faster than the body is able to repair them•Replication errors can cause mutations (DNA Polymerase does not detect them all).•Mutagens, such as UV ray and chemicals, can cause mutations.

– UV light breaks the T-A bond and causes the them to bond incorrectly. This can result in cancer.

•Some cancer drugs use mutagenic properties to kill cancer cells.

8.7 Mutations

Review

• Where/when do most mutations occur?• What is the difference between a point mutation (1 type)

and a frameshift mutation (2 types)? • Contrast the results of a point mutation and a frameshift

mutation• Why aren’t mutations in body cells passed on to the next

generation?• What’s the big deal? Doesn’t the DNA have

proofreading/repair mechanisms?• THINK: How could a mutated gene produce a shorter

protein than the normal gene?