CH 6: Genetics of Bacteria and Bacteriophage

What is a mutation?

A heritable change in DNA sequence.

What are spontaneous mutations?

Mutations that occur naturally without external influence.

What are induced mutations?

Mutations caused by external factors such as chemicals or radiation.

What is a somatic mutation?

A mutation occurring in non-gamete cells; not inherited.

What is a germ-line mutation?

A mutation occurring in gametes; can be passed to offspring.

What is a point mutation?

A change in a single nucleotide pair.

What is a base substitution?

Replacement of one nucleotide with another.

What is a transition mutation?

Purine ↔ purine or pyrimidine ↔ pyrimidine substitution.

What is a transversion mutation?

Purine ↔ pyrimidine substitution.

What is a missense mutation?

Base substitution causing a different amino acid.

What is a silent mutation?

Base substitution that does not change the amino acid.

What is a nonsense mutation?

A base change converting a codon to a stop codon.

What is a frameshift mutation?

Insertion or deletion that shifts the reading frame.

What are neutral mutations?

Mutations with no effect on organismal fitness.

What are loss-of-function mutations?

Mutations that reduce or eliminate gene product activity.

What are gain-of-function mutations?

Mutations that increase or create new gene product activity.

What is a dominant-negative mutation?

A mutant allele that interferes with the function of the wild-type allele.

What is a lethal mutation?

A mutation that disrupts essential processes and causes death.

What is a conditional mutation?

A mutation whose effects occur only under certain environmental conditions.

What is a temperature-sensitive mutation?

A mutation that produces a phenotype only at restrictive temperatures.

What is a spontaneous tautomeric shift?

A temporary base structural shift that can cause mismatched pairing.

What is depurination?

Loss of a purine base from DNA.

What is deamination?

Removal of an amino group from a nucleotide (e.g.

What is oxidative DNA damage?

DNA damage caused by reactive oxygen species.

What are transposable elements?

Mobile genetic elements that can move within and between genomes.

What is insertional mutagenesis?

A mutation caused by transposon insertion disrupting a gene.

What is a mutagen?

Any agent that increases mutation frequency.

What are base analogs?

Chemicals structurally similar to nucleotides that can be incorporated into DNA.

What is 5-bromouracil?

A base analog that can pair with A or G

What are alkylating agents?

Mutagens that add alkyl groups to bases

What are intercalating agents?

Flat molecules that insert between base pairs and cause insertions/deletions.

What is UV radiation’s main DNA damage?

Formation of pyrimidine dimers (usually thymine dimers).

What type of damage does ionizing radiation cause?

Double-strand DNA breaks and chromosome fragmentation.

What is proofreading?

DNA polymerase’s ability to correct mismatched bases during replication.

What is mismatch repair?

Repair system that fixes errors missed by proofreading by replacing the incorrect base.

How does mismatch repair distinguish old vs new strands?

By recognizing DNA methylation patterns on the parental strand.

What is base excision repair (BER)?

A repair pathway removing damaged bases via DNA glycosylases.

What is nucleotide excision repair (NER)?

Pathway removing bulky lesions like thymine dimers.

What disease is associated with defective NER?

Xeroderma pigmentosum (extreme UV sensitivity).

What is double-strand break repair?

Repair mechanism including homologous recombination or non-homologous end joining.

What is homologous recombination repair?

Error-free repair using a sister chromatid as template.

What is non-homologous end joining (NHEJ)?

Error-prone repair joining DNA ends without template.

What is the SOS response?

A bacterial error-prone repair system activated under severe DNA damage.

What is the Ames test used for?

To test chemicals for mutagenic potential.

What organism is used in the Ames test?

Auxotrophic Salmonella strains.

What indicates a positive Ames test?

Increased number of His+ revertant colonies.

What is a forward mutation?

Changes wild-type allele to mutant form.

What is a reverse mutation (reversion)?

Converts mutant allele back to wild-type.

What is a suppressor mutation?

A second mutation that restores the wild-type phenotype.

What is intragenic suppression?

Both mutations occur within the same gene.

What is intergenic suppression?

A mutation in a different gene compensates for the first mutation.

What are trinucleotide repeat expansions?

Repeated sequence expansions causing disease (e.g.

What is anticipation?

Earlier onset and severity of disease in successive generations due to repeat expansion.

What type of mutation causes sickle cell anemia?

A missense mutation in the β-globin gene (Glu → Val).

What is oxidative deamination?

Spontaneous conversion of cytosine to uracil.

What is photoreactivation repair?

Enzyme photolyase uses light energy to split thymine dimers.

What is translesion synthesis?

Replication across damaged DNA using low-fidelity polymerases.

What are retrotransposons?

Mobile elements that move via an RNA intermediate.

What is LINE-1?

A common long interspersed nuclear element in humans.

What is a pseudogene?

A nonfunctional gene copy often created by retrotransposition.

What is a mutator phenotype?

Increased overall mutation rate in cells

What is genome instability?

High mutation frequency across the genome due to repair defects.

What is a bacterial chromosome?

A single circular double-stranded DNA molecule.

What is a plasmid?

A small independently replicating circular DNA molecule.

What is an episome?

A plasmid that can integrate into the bacterial chromosome.

What is vertical gene transfer?

Transmission of genetic material from parent to offspring.

What is horizontal gene transfer?

Transfer of DNA between individuals other than parent → offspring.

What are the three mechanisms of bacterial gene transfer?

Conjugation transformation and transduction.

What is conjugation?

Direct transfer of DNA between bacteria via cell-to-cell contact.