Chapter 15 | Gene Mutation, DNA Repair, and Transposition

Somatic Mutation

A mutation occurring in non–sex cells; not inherited by offspring

Germ-Line Mutation

A mutation in gametes; heritable and often more harmful due to transmission to the next generation

Loss-of-Function Mutation

An allele that produces a nonfunctional protein

Null Mutation

A mutation resulting in no gene product at all

Morphological Mutation

A mutation that alters a visible physical trait

Biochemical Mutation

A mutation affecting a biochemical pathway (e.g., Agouti mice)

Nutritional Mutation (Auxotrophic)

Mutation preventing synthesis of a required nutrient; auxotrophs must obtain it from the environment

Prototrophic Phenotype

Wild-type ability of an organism to synthesize all required nutrients

Haploinsufficiency

When one functional allele is insufficient to produce a wild-type phenotype (e.g., digit length)

Behavioral Mutation

A mutation affecting organismal behavior (e.g., low-serotonin phenotype from defective monoamine oxidase)

Conditional Mutation

A mutation expressing a phenotype only under certain conditions

Temperature-Sensitive Mutation

A mutation that produces a mutant phenotype at non-permissive temperatures but appears wild-type at permissive temperatures

Point Mutation (SNP)

A single nucleotide change in the DNA sequence

Silent Mutation

A nucleotide substitution that does not alter the amino acid sequence

Missense Mutation

A nucleotide substitution causing an amino acid change in the protein

Nonsense Mutation

A nucleotide substitution producing a premature stop codon, creating an incomplete protein

Transition Mutation

A substitution between two purines or two pyrimidines; occurs more frequently than transversions

Transversion Mutation

A substitution between a purine and a pyrimidine

Frameshift Mutation

Alteration of the reading frame caused by insertion or deletion of nucleotides

Intragenic Suppressor Mutation

A second mutation within the same gene that compensates for the original mutation

Intergenic Suppressor Mutation

A second mutation in a different gene that restores a wild-type phenotype through pathway compensation

Promoter Mutation

A mutation altering promoter sequences, potentially affecting transcription initiation

Splicing Mutation

A mutation disrupting normal intron removal or exon joining

Cryptic Splice Site

A new, unintended splice site created by mutation, causing abnormal splicing

Tautomeric Shifts

Temporary proton shifts in bases (keto ↔ enol, amino ↔ imino) leading to abnormal base pairing. During replication, changed pairing causes transition mutations in daughter strands

AP Site

A site missing a nitrogenous base due to glycosidic bond breakage; replication inserts a random base

Deamination

Loss of amino groups from bases (e.g., cytosine → uracil), altering base-pairing properties

Oxidative DNA Damage

Damage by free radicals that can break DNA or alter bases

Transposon-Induced Mutation

Mobile genetic elements insert into new genomic locations, causing disruptive insertions

Base Analogs

Molecules resembling normal bases but with incorrect pairing properties

Alkylating Agenets

Mutagens that add alkyl groups to bases, altering their pairing behavior

Polymerase Slippage

Errors in repetitive DNA causing insertions (expansions) or deletions due to hairpin formation

Acridine Dyes

Intercalating agents that distort DNA and cause frameshift mutations

Ionizing Radiation

High-energy radiation producing free radicals that damage DNA bonds

UV-Induced Dimers

UV radiation forms pyrimidine dimers (e.g., thymine-thymine), blocking replication and leading to error-prone repair

Induced Mutation

A mutation resulting from external DNA damage rather than natural cellular processes

AMES Test

A bacterial assay that determines whether a chemical induces mutations

His^- Auxotroph in AMES Test

Strain cannot synthesize histidine; reversion to his⁺ indicates a mutagenic event

Mutagenicity Assessment

More revertant colonies indicate a stronger mutagen; fewer colonies indicate lower mutagenicity

Liver Enzyme Activation in AMES Test

Chemicals are treated with liver enzymes to test whether their metabolic byproducts are mutagenic