Genetics - Chapter 19: Gene Mutation and DNA Repair

mutation

a permanent change in the genetic material that can be passed from cell to cell or, if it occurs in reproductive cells, from parent to offspring

point mutation

a change in a single base pair within DNA

base substitution

a point mutation in which one base is substituted for another

transition

a point mutation involving a change of a pyrimidine to another pyrimidine (e.g., C to T) or a purine to another purine (e.g., A to G)

transversion

a point mutation in which a purine is interchanged with a pyrimidine, or vice versa

silent mutation

a mutation that does not alter the amino acid sequence of the encoded polypeptide even though the base sequence has changed

missense mutation

a base substitution that leads to a change in the amino acid sequence of the encoded polypeptide

nonsense mutation

a mutation that involves a change from a normal codon to a stop codon

frameshift mutation

a mutation that involves the addition or deletion of a number of nucleotides not divisible by 3, which shifts the reading frame of the codons downstream from the mutation

neutral mutation

a mutation that has no detectable effect on protein function or no detectable effect on the survival of the organism

up promoter mutation

a mutation in a promoter that increases the rate of transcription

down promoter mutation

a mutation in a promoter that inhibits the rate of transcription

wild type

a relatively prevalent genotype in a natural population

mutant allele

allele that has been created by altering a wild-type allele by mutation

reversion

a mutation that returns a mutant allele back to a wild-type allele

deleterious mutation

a mutation that is detrimental with regard to its effect on phenotype

lethal mutation

a mutation that produces a lethal allele that may cause the death of a cell or an organism

beneficial mutation

a mutation that enhances the survival or reproductive success of an organism

conditional mutant

a mutant whose phenotype depends on the environmental conditions, such as a temperature-sensitive mutant

suppressor (suppressor mutation)

a mutation at a second site that suppresses the phenotypic effects of another mutation

intragenic suppressor

a suppressor mutation that is within the same gene as the first mutation that it suppresses

intergenic suppressor

a suppressor mutation that is in a different gene from the gene that contains the first mutation

breakpoint

a region where two chromosome pieces break and rejoin with other chromosome pieces

position effect

a change in phenotype that occurs when the location of a gene is changed from one chromosomal site to a different one

germ line

cells that give rise to gametes

germ-line mutation

a mutation in a cell of the germ line

somatic cell

any cell of the body except for germ-line cells that give rise to gametes

somatic mutation

a mutation in a somatic cell

genetic mosaic

an individual that has somatic regions that differ genotypically from each other

replica plating

a technique in which replicas of bacterial colonies are transferred to new growth plates

random mutation theory

according to this theory, mutations are a random process-they can occur in any gene and do not involve exposure of an organism to a particular condition that selects for specific types of mutations

hot spots

regions within a gene that are more likely to mutate than others

spontaneous mutation

a change in DNA structure that results from natural biological or chemical processes

induced mutation

a mutation caused by an environmental agent

depurination

the removal of a purine base from DNA

apurinic site

a site in DNA that is missing a purine base

deamination

the removal of an amino group from a molecule, for example: the removal of an amino group from cytosine produces uracil

tautomeric shift

a temporary change in chemical structure, such as an alternation between the keto and enol forms of the bases that are found in DNA

tautomers

chemically similar forms of certain small molecules, such as bases, which can spontaneously interconvert

reactive oxygen species (ROS)

products of oxygen metabolism in all aerobic organisms that can damage cellular molecules, including DNA, proteins, and lipids

oxidative stress

an imbalance between the production of reactive oxygen species (ROS) and an organism's ability to break them down

oxidative DNA damage

changes in DNA structure that are caused by reactive oxygen species (ROS)

trinucleotide repeat expansion (TNRE)

a type of mutation that involves an increase in the number of tandemly repeated trinucleotide sequences

anticipation

the phenomenon in which the severity of an inherited disease tends to get worse in later generations

mutagen

an agent that causes alterations in the structure of DNA

nitrous acid

a type of chemical mutagen that deaminates bases, changing amino groups to keto groups

nitrogen mustard

an alkylating agent that can cause mutations in DNA

ethyl methanesulfonate (EMS)

a type of chemical mutagen that alkylates bases (i.e., attaches methyl or ethyl groups)

acridine dye

a type of chemical mutagen that causes frameshift mutations

proflavin

an acridine dye, which is a chemical mutagen that causes frameshift mutations

5-bromouracil (5BU)

a base analog that acts as a chemical mutagen

2-aminopurine

a base analog that acts as a chemical mutagen

thymine dimer

two adjacent thymine bases in a DNA strand that have become covalently linked

mutation rate

the likelihood that a gene will be altered by a new mutation

mutation frequency

the number of mutant genes divided by the total number of genes within the population

Ames test

a test using strains of a bacterium, Salmonella typhimurium, to determine if a substance is a mutagen

photolyase

an enzyme found in bacteria, fungi, most plants, and some animals that can recognize and split thymine dimers, which returns the DNA to its original condition

photoreactivation

a type of DNA repair mechanism of thymine dimers that involves photolyase and requires light

alkyltransferase

an enzyme that can remove methyl or ethyl groups from guanine bases

base excision repair (BER)

a type of DNA repair in which a modified base is removed from a DNA strand. Following base removal, a short region of the DNA strand is removed, which is then resynthesized using the complementary strand as a template

DNA N-glycosylase

an enzyme that can recognize an abnormal base and cleave the bond between it and the sugar in the DNA backbone

AP endonuclease

a DNA repair enzyme that recognizes a DNA region that is missing a base and makes a cut in the DNA backbone near that site

nucleotide excision repair (NER)

a DNA repair system in which several nucleotides in the damaged strand are removed from the DNA and the undamaged strand is used as a template to resynthesize a normal strand

base pair mismatch

when two bases opposite each other in a double helix do not conform to the AT/GC rule, i.e. if A were opposite C

mismatch repair system

a DNA repair system that recognizes base pair mismatches and repairs the newly made daughter strand that contains the incorrect base

homologous recombination repair (HRR) (homology-directed repair)

mechanism for repairing double-strand breaks that occurs when the DNA strands from a sister chromatid are used to repair a lesion in the other sister chromatid

non-homologous end joining (NHEJ)

a repair mechanism for double-strand breaks in which the ends of the DNA are pieced back together

translesion synthesis (TLS)

the synthesis of DNA over a template strand that harbors some type of DNA damage. This occurs via lesion-replicating polymerases

error-prone replication

a form of DNA replication carried out by lesion-replicating polymerases that results in a high rate of mutation