micro 11.5

Mutation

A heritable change in the nucleotide sequence of DNA.

Wild-Type

The normal genotype or phenotype most commonly found in nature.

Mutant

An organism or cell that carries one or more mutations.

Spontaneous Mutation

A mutation that occurs naturally due to errors in DNA replication or normal cellular processes.

Induced Mutation

A mutation caused by exposure to physical, chemical, or biological mutagens.

Mutagen

Any agent that increases the rate of mutations in DNA.

Point Mutation

A mutation involving a change in a single nucleotide base pair.

Base Substitution

A type of point mutation in which one nucleotide is replaced by another.

Silent Mutation

A base substitution that does not change the amino acid encoded.

Missense Mutation

A base substitution that changes one amino acid to another in a protein.

Nonsense Mutation

A base substitution that converts an amino acid codon into a stop codon, producing a shortened protein.

Frameshift Mutation

A mutation caused by the insertion or deletion of nucleotides that shifts the reading frame.

Insertion Mutation

A mutation in which one or more nucleotides are added to a DNA sequence.

Deletion Mutation

A mutation in which one or more nucleotides are removed from a DNA sequence.

Reading Frame

The grouping of nucleotides into codons during translation.

Forward Mutation

A mutation that changes the wild-type genotype or phenotype into a mutant form.

Reverse Mutation (Back Mutation)

A mutation that restores the original wild-type DNA sequence or phenotype.

Suppressor Mutation

A second mutation that compensates for the effects of an earlier mutation.

DNA Repair

Cellular mechanisms that detect and correct DNA damage or replication errors.

Proofreading

The exonuclease activity of DNA polymerase that removes incorrectly paired nucleotides during DNA replication.

Direct Repair

A DNA repair mechanism that reverses DNA damage without replacing nucleotides.

Excision Repair

A DNA repair process in which damaged DNA is removed and replaced with newly synthesized DNA.

Mismatch Repair

A repair system that corrects incorrectly paired nucleotides remaining after DNA replication.

Photoreactivation

A direct DNA repair mechanism in which the enzyme photolyase uses visible light to repair UV-induced thymine dimers.

Photolyase

The enzyme that repairs thymine dimers during photoreactivation.

Thymine Dimer

A DNA lesion caused by ultraviolet (UV) light in which two adjacent thymine bases become covalently linked.

Chemical Mutagen

A chemical substance that causes DNA mutations by altering nucleotide structure or DNA replication.

Physical Mutagen

A physical agent, such as UV light or ionizing radiation, that damages DNA and increases mutation rates.

Biological Mutagen

A biological agent, such as a transposable element or virus, that can cause mutations in DNA.

Transposon (Transposable Element)

A DNA sequence that can move from one location to another within a genome, potentially causing mutations.