Gene Mutation and DNA Repair Lecture Flashcards

Comprehensive vocabulary flashcards covering gene mutations, their consequences, causes (spontaneous and induced), and biological repair mechanisms based on Dr. O.H. Ajetunmobi's lecture.

Mutation

A heritable change in the genetic material that provides allelic variations and serves as the foundation for evolutionary change.

Point mutation

A change in a single base pair involving a base substitution.

Transition

A type of point mutation involving a change of a pyrimidine ($C, T$) to another pyrimidine or a purine ($A, G$) to another purine; these are more common than transversions.

Transversion

A type of point mutation involving a change of a pyrimidine to a purine or vice versa.

Silent mutations

Mutations that do not alter the amino acid sequence due to the degeneracy of the genetic code.

Missense mutations

Mutations that alter the amino acid sequence, such as the one causing sickle-cell anemia.

Nonsense mutations

Mutations that change a codon to a stop codon, resulting in a truncated polypeptide.

Up promoter mutations

Mutations in noncoding sequences that increase the rate of transcription.

Down promoter mutations

Mutations in noncoding sequences that decrease the rate of transcription.

Reverse mutation (reversion)

A mutation that changes a mutant allele back to the wild-type genotype.

Neutral mutation

A mutation that does not alter protein function.

Deleterious mutation

A mutation that lowers the chance of survival and reproduction; an extreme version is a lethal mutation.

Conditional mutation

A mutation that affects the phenotype only under specific conditions, such as temperature-sensitive ($ts$) mutants that grow at $33$ to $38^{\circ}C$ but not at $40$ to $42^{\circ}C$.

Suppressor mutation

A second mutation that affects the phenotypic expression of a first mutation, occurring at a different site than the first.

Intragenic suppressor

A suppressor mutation where the second mutation is located in the same gene as the first.

Intergenic suppressor

A suppressor mutation where the second mutation occurs in a different gene than the first.

Position effect

A change in gene expression caused by moving a gene to a new location, such as near a different regulatory sequence or a heterochromatic region.

Genetic mosaic

An individual with somatic cells that are genotypically different from each other due to somatic mutations occurring during development.

Mutagen

A chemical or physical agent known to alter DNA and cause induced mutations.

Depurination

The removal of a purine (adenine or guanine) from the DNA, creating an unstable apurinic site; if unrepaired, there is a $75\%$ chance of mutation.

Deamination

The removal of an amino group from a base; for example, deamination of cytosine produces uracil, while deamination of 5-methylcytosine produces thymine.

Tautomeric shift

A temporary change in base structure (such as keto to enol or amino to imino) that promotes mismatched base pairs like $A-C$ and $G-T$ if it occurs prior to replication.

8-oxoG

An oxidized form of guanine caused by reactive oxygen species that base pairs with adenine, causing a $G-C$ to $T-A$ functional mutation.

Trinucleotide repeat expansion (TNRE)

A type of mutation where the number of tandem trinucleotide sequences increases across generations, associated with disorders like Huntington disease.

Anticipation

A feature of TNRE disorders where the severity of the disease worsens and the age of onset may decrease in future generations.

Base analogs

Chemical mutagens like 5-bromouracil ($5BU$) that are incorporated into daughter strands during DNA replication in place of standard bases.

Intercalating agents

Chemicals with flat planar structures, such as Proflavine, that insert into the double helix and cause frameshift mutations.

Ionizing radiation

High energy radiation like X-rays and gamma rays that creates free radicals and causes single- or double-strand breaks in the DNA backbone.

Nonionizing radiation

UV light, which has less energy than ionizing radiation and causes the formation of cross-linked thymine dimers.

Direct repair

A repair system where an enzyme, such as photolyase, recognizes an incorrect alteration and directly converts it back to the correct form.

Mismatch repair

A system that recognizes and fixes base-pair mismatches that escape the $3'$ to $5'$ proofreading ability of DNA polymerase.

Translesion syntheses (TLS)

A process where specialized polymerases with loose flexible pockets replicate over DNA lesions, though they often exhibit low fidelity and higher mutation rates.