Biology(Mutations)

What is a mutation?

A permanent change in the DNA nucleotide sequence.

Are all mutations harmful?

No. Mutations may be harmful, beneficial, or neutral.

What are spontaneous mutations?

Mutations that arise naturally, often due to DNA replication errors or spontaneous chemical changes.

What are induced mutations?

Mutations caused by external mutagens such as UV light, X-rays, or chemicals.

Difference between germline and somatic mutations?

• Germline: Occur in gametes or their precursors and can be inherited.

• Somatic: Occur in body cells and are not inherited.

What is a point mutation?

A mutation affecting a single nucleotide pair.

What is a silent mutation?

A nucleotide change that does not change the amino acid because of the degeneracy of the genetic code.

Why can silent mutations occur?

Because multiple codons can encode the same amino acid.

What is a missense mutation?

A mutation that changes one amino acid into another.

What is a nonsense mutation?

mutation that converts an amino acid codon into a stop codon, producing a truncated protein.

What is a frameshift mutation?

A mutation caused by insertion or deletion of nucleotides not divisible by three, changing the reading frame.

Why are frameshift mutations usually severe?

They alter all downstream codons and often introduce premature stop codons.

What is an insertion?

Addition of one or more nucleotides into DNA.

What is a deletion?

Removal of one or more nucleotides from DNA.

What is an in-frame mutation?

An insertion or deletion of a multiple of three nucleotides, preserving the reading frame.

Why is DNA repair necessary?

To maintain genome stability and prevent accumulation of mutations.

Which enzyme proofreads DNA during replication?

DNA polymerase.

When does proofreading occur?

During DNA replication.

Does proofreading eliminate all mutations?

No, but it greatly reduces the mutation rate.

What happens if DNA repair fails?

Mutations accumulate, increasing the risk of abnormal proteins, cell death, or cancer.

What is a mutagen?

Any physical or chemical agent that increases the mutation rate.

Give examples of mutagens.

• UV radiation

• X-rays

• Gamma rays

• Cigarette smoke

• Certain chemicals

What type of DNA damage is commonly caused by UV radiation?

Thymine dimers.

Why are thymine dimers harmful?

They distort DNA and interfere with replication and transcription if unrepaired.

Difference between gene mutations and chromosomal mutations?

Gene mutations affect one gene or a few nucleotides; chromosomal mutations affect large chromosome segments or whole chromosomes.

What is a chromosomal deletion?

Loss of a chromosome segment.

What is duplication?

Repetition of a chromosome segment.

What is inversion?

A chromosome segment reverses orientation after breaking and reinserting.

What is translocation?

A chromosome segment moves to another chromosome.

What is aneuploidy?

An abnormal number of chromosomes.

What causes aneuploidy?

Nondisjunction during meiosis.

What is nondisjunction?

Failure of homologous chromosomes or sister chromatids to separate properly.

What is trisomy?

Three copies of one chromosome.

What is monosomy?

Only one copy of a chromosome instead of two.

Cause of Down syndrome?

Trisomy 21 caused by nondisjunction.

What is a proto-oncogene?

A normal gene that promotes cell growth under normal conditions.

What is an oncogene?

A mutated proto-oncogene that promotes uncontrolled cell division.

What is a tumor suppressor gene?

A gene that normally limits cell division or promotes DNA repair.

What happens if a tumor suppressor gene loses function?

Cells are more likely to divide uncontrollably.

Which mutation type usually has the least effect?

Silent mutation.

Which mutation type usually has the greatest effect?

Frameshift mutation.

Which mutation is inherited?

Germline mutation.

Why is the genetic code called degenerate?

Because multiple codons can encode the same amino acid.

Explain the difference between missense, nonsense, and frameshift mutations.

• Missense: One amino acid changes.

• Nonsense: A stop codon is created.

• Frameshift: The reading frame changes, altering downstream amino acids.