Lesson 17: Gene Mutation, DNA Repair and Homologous Recombination

mutation rate

the rate at which mutations occur per gene per unit of time

adaptive mutation hypothesis

a disproven theory of the source of gene mutations proposing that mutated copies of genes were available in the genome or could rapidly occur in the genome given specific changes in the physical environment of an organism

random mutation hypothesis

the correct theory that gene mutations occur at random

somatic mutation

a mutation occurring in a somatic cell of an organismg

germ-line mutation

a mutation present in a sperm, pollen, or egg

base pair mutation

a mutation in a single pair of nucleotides

transition mutation

a type of DNA base pair substitution in which one purine replaces the other or one pyrimidine replaces the other

transversion mutation

a type of DNA base substitution mutation in which a purine substitutes for a pyrimidine or vice versa

synonymois mutation

a base substitution mutation that changes one codon to a synonymous codon and doesn’t alter the amino acid sequence of a polypeptide

missense mutation

a DNA base pair substitution mutation that leads to production of a polypeptide in which one amino acid substitutes for another

nonsense mutation

a type of point mutation producing a stop codon in mRNA

frameshift mutation

the insertion or deletion of DNA base pairs resulting in translation of mRNA in an incorrect reading frame

reversion mutation

a mutation that alters a mutant to wild-type sequence and function

strand slippage

during DNA replication, a mutational event leading to increased or decreased numbers of repeating nucleotides in newly synthesized DNA and caused by slippage of DNA polymerase on the template strand or slippage of the newly synthesized strand on DNA polymerase

trinucleotide repeat expansion disorder

a hereditary disorder caused by a mutant gene containing an increased number of repeats of a DNA trinucleotide sequence

deamination

a DNA lesion resulting in the loss of an amino group from a nucleotide base

depurination

a DNA lesion occurring when a deoxyribose molecule loses its purine nucleotide base

apurinic site

the location of a nucleotide that has lost its purine base

mutagens

a chemical, physical, or biological agent capable of damaging DNA and creating a mutation

nucleotide base analog

a compound with a size and shape that mimics a natural nucleotide base

DNA intercalation agents

mutagenic compounds of a size and shape that allow them to access to the space between nucleotide base pairs, thereby distorting the DNA duplex and potentially causing insertion or deletion mutations

thymine dimer

the specific type of lesion formed on DNA due to exposure to UV irradiation

Ames test

a lab method commonly used to determine whether a compound or one of its breakdown products is mutagenic

photoreactive repair

a mechanism of DNA damage repair in bacteria that uses visible light to provide the energy to remove the damage done by UV irradiation

base excision repair

DNA repair that excises a damaged nucleotide base and then replaces the entire nucleotide

nucleotide excision repair

a mechanism of DNA damage repair in which a segment of one strand containing damaged nucleotides is excised and replaced

UV repair

a multiprotein DNA damage repair system that corrects lesions caused by exposure to UV irradiation

mismatch repair

the DNA repair process that repairs noncomplementary base pairs that occur through errant DNA replication or through nucleotide base modification, restores normal complementary base pairing

double stranded breaks

breakage of phosphodiester bonds on both strands of DNA; associated with DNA damage or with the initial steps of the process leading to homologous recombination

double-strand break repair

following phosphodiester bond breakage on both strands of a DNA duplex, a mechanism of DNA damage repair

nonhomologous end joining

an error-prone mechanism of double stranded DNA break repair in eukaryotic genomes in which damaged nucleotides are removed and blunt end of strands are joined

synthesis dependent strand annealing

an error-free mechanism for repair of DNA double strand breaks occurring after the completion of DNA replication and utilizing strand invasion to provide wild-type sequences for repair

strand invasion

during synthesis dependent strand annealing and meiotic recombination, the entry of the 3’ end of a displaced DNA into the intact sister chromatid

displacement loop

during DNA damage repair and homologous recombination, the displacement of a single strand of DNA by strand invasion

homologous recombination

exchange of genetic information between homologous DNA molecules

Holliday model

a model intended to explain meiotic recombination at a molecular level

RecBCD pathway

a complex of three bacterial proteins that cut DNA and facilitate homologous recombination

Holliday junction

a DNA structure that forms during meiotic recombination in which single strands are crossed over between nonsister chromatids of homologous chromosomes

heteroduplex region

a stretch of DNA where the two strands come from different sources and are not perfectly complementaryhet

heteroduplex DNA

a DNA duplex created during homologous recombination by combining complementary strands of DNA from nonsister chromatids

double Holliday junctions

an intermediate structure temporarily connecting chromatids of homologous chromosomes that forms during homologous recombination

opposite sense resolution

one possible process for resolving the DNA connections between homologous chromosomes following crossover as part of homologous recombination

same sense resolution

one of the possible patterns for resolving a Holliday junction to separate homologous chromosomes before meiotic anaphase

transposable genetic elements

a class of DNA sequences that can move from one chromosome location to another, either by excision and reinsertion or by replication and reinsertion of the replicated copy

transposition

the process by which mobile genetic elements move from one portion of a genome to another

terminal inverted repeats

identical sequences found at both ends of a transposable genetic element

flanking direct repeats

identical repetitive sequences flanking the site of insertion of transposable genetic elements

transposase

the enzyme produced by transposons that cut DNA to allow the excision and insertion of the transposon

DNA transposons

one type of transposable genetic element encoding a transposase and capable of transposition

retrotransposons

a transposable genetic element uses reverse transcriptase to transpose through an RNA intermediate

replicative transposition

transposition carried out by replicating a copy of a transposable element and inserting the copy in a new genome location

nonreplicative transposition

a transposable genetic element that transposes by excision from the original genome location, followed by insertion into a new location

insertional inactivation

a process of mutation in which the insertion of DNA into a gene renders it nonfunctional

insertion sequences

a bacterial DNA sequence that is the target of insertion of a transposable genetic element of is the site of integration of a plasmid

composite transposon

in bacteria, a transposable element containing multiple genes located between terminal insertion sequences

noncomposite transposon

bacterial transposable genetic elements that lack insertion sequences

long terminal repeats

arrays of scores to hundreds of nucleotides that bracket the ends of retroviruses integrated into host chromosomes