Mutation, DNA Repair and Genome Instability: every key term you need (+ practice quiz)
25 flashcard terms for Genetics Topic 5, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
A change affecting a single base pair, the most common class and the one whose consequences depend heavily on reading frame position.
Transition and transversion
A transition swaps bases of the same ring type and a transversion swaps between types. Transitions are more frequent despite there being more possible transversions.
Silent mutation
A base change that leaves the encoded amino acid unchanged, usually at a third codon position, though it can still alter splicing or translation speed.
Missense mutation
A base change that substitutes one amino acid for another, with effects ranging from none to complete loss depending on the residue's role.
Nonsense mutation
A change creating a premature stop codon, which truncates the product and often triggers destruction of the transcript.
Frameshift mutation
An insertion or deletion of a number of bases not divisible by three, which garbles everything downstream and usually reaches an early stop.
Loss-of-function allele
An allele producing reduced or no activity. It is usually recessive because one working copy often supplies enough product.
Gain-of-function allele
An allele producing new or unregulated activity, typically dominant because the change cannot be masked by a normal copy.
Dominant negative allele
A defective product that poisons the normal one, most often in proteins that work as multi-subunit complexes.
Spontaneous deamination
Loss of an amino group converting cytosine to uracil, a frequent lesion that repair systems recognize because uracil does not belong in the duplex.
Depurination
Loss of a base leaving an empty site in the backbone. It happens thousands of times per cell per day and is mutagenic if copied before repair.
Tautomeric shift
A rare alternative base form that pairs incorrectly. If it occurs during copying, the mismatch becomes a permanent change after another round.
Intercalating agent
A flat molecule that slips between stacked bases and distorts the helix, characteristically causing single-base insertions or deletions.
Ultraviolet damage
Adjacent pyrimidines become covalently joined, blocking the replication machinery until the lesion is removed.
Ames test
Screens a compound for mutagenicity by counting reversion events in bacteria, often after adding liver extract to mimic metabolic activation.
Mismatch repair
Corrects errors missed by proofreading, using strand marks to tell which base is new and therefore which one to replace.
Base excision repair
Removes a single damaged base with a specific glycosylase, then rebuilds the short gap, the main defence against oxidation and deamination.
Nucleotide excision repair
Removes a short stretch containing a bulky distorting lesion and resynthesizes it, the pathway that clears ultraviolet damage.
Direct reversal repair
Chemically undoes a lesion without excising anything, an efficient but narrowly specific route available for only a few damage types.
Translesion synthesis
A specialized low-accuracy polymerase copies past a lesion so replication can finish, trading fidelity for survival.
Double-strand break consequences
The most dangerous lesion, because both strands are lost as templates; repair choice determines whether the sequence is restored or scarred.
Mutation rate versus frequency
Rate is how often new changes arise per generation; frequency is how common an allele already is. Selection and drift separate the two.
Trinucleotide repeat expansion
Repeat tracts that grow between generations, producing disorders that appear earlier and more severely down a pedigree.
Transposable element
A sequence that can move within a genome, disrupting genes where it lands and providing repeats that promote later rearrangements.
Two-hit model
The requirement that both copies of a protective gene be lost for a tumour to develop, which explains why inherited predisposition raises risk and lowers the age of onset.