Genetics Chapter 14 - Gene Mutation, DNA Repair, and Transposition

What is a mutation?

A change in DNA sequence

Spontaneous mutation?

Occurs naturally from normal cellular processes

Induced mutation?

Caused by external agents (mutagens)

Somatic mutation?

Occurs in body cells; NOT inherited

Germ-line mutation?

Occurs in gametes; inherited

Autosomal mutation?

On non-sex chromosomes

X-linked mutation?

On X chromosome

Point mutation?

Single base pair change

Transition mutation?

Purine to purine OR pyrimidine to pyrimidine

Transversion mutation?

Purine to pyrimidine

Frameshift mutation?

Insertion/deletion NOT multiple of 3; shifts reading frame

Missense mutation?

Changes amino acid

Nonsense mutation?

Creates STOP codon

Silent mutation?

No change in amino acid

Conditional mutation?

Effect depends on environment

Lethal mutation?

Causes death

Replication error cause?

DNA polymerase inserts wrong base

Replication slippage leads to?

Insertions/deletions

Oxidative damage cause?

Cellular byproducts damage DNA

Transposons cause?

Insert into genome - mutation

What is a tautomeric shift?

Temporary change in base structure - abnormal pairing

Result of tautomeric shift?

Mutation after replication

Most common cause of spontaneous mutation?

Depurination and deamination

Depurination?

Loss of purine base (A or G)

Deamination example?

Cytosine to uracil

What is a mutagen?

Agent that causes mutations

Base analogs do what?

Substitute for normal bases - mispairing

Acridine dyes cause waht?

Frameshift mutations

Example acridine dye?

Ethidium bromide

UV radiation causes what?

Pyrimidine (thymine) dimers

Effect of dimers?

Distort DNA - replication errors

Ionizing radiation examples?

X-rays, gamma rays

Effect of ionizing radiation?

Point mutations and chromosomal damage

Why is DNA repair important?

Fixes mutations to maintain genome stability

Which enzyme proofreads?

DNA polymerase III

Error rate before proofreading?

~1 in 100,000

% of errors corrected after proofreading?

~99%

When does postreplication repair occur?

After replication skips lesion

Mechanism of postreplication repair?

Uses homologous recombination

What does Nucleotide Excision Repair (NER) fix?

Bulky DNA damage (like dimers)

Steps of Nucleotide Excision Repair (NER)?

1. Nuclease removes damaged DNA, 2. DNA polymerase fills gap, 3. DNA ligase seals nick

Purpose of Ames test?

Detect mutagenicity of chemicals

What organism is used in Ames test?

Salmonella Typhimurium

Why are liver enzymes added in Ames test?

Some chemicals become mutagenic after metabolism

What indicates a mutagen in Ames test?

Increased number of revertant colonies