Genetics - Chapter 18
thymine dimer
a DNA lesion involving a covalent linkage between two adjacent thymine bases in a DNA strand
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
mismatch repair system/methyl-directed mismatch repair
a DNA repair system that detects a mismatch and specifically removes the segment from the newly made daughter strand
2-amniopurine
a base analog that acts as a chemical mutagen
5-bromouracil (5BU)
a base analog that acts as a chemical mutagen
missense mutations
a base substitution that leads to a change in the amino acid sequence of the encoded polypeptide
spontaneous mutations
a change in DNA structure that results from random abnormalities in biological processes
point mutation
a change in a single base pair within DNA
tautomeric shift
a change in chemical structure, such as an alteration between the keto and enol forms of the bases that are found in DNA
position effect
a change in phenotype that occurs when the position of a gene is changed from one chromosomal site to a different location
error-prone replication
a form of DNA replication carried out by lesion-replicating DNA polymerases that results in a high rate of mutation
germ line
a lineage of cells that gives rise to gametes
conditional mutants
a mutant whose phenotype depends on the environmental conditions, such as a temperature-sensitive mutant
suppressor mutation/suppressor
a mutation at a second site that suppresses the phenotypic effects of another mutation
induced mutations
a mutation caused by environmental agents
germ-line mutation
a mutation in a cell of the germ line
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
somatic mutation
a mutation in a somatic cell
polar mutation
a mutation in an operon that affects the expression of another gene that is found downstream in the operon
silent mutations
a mutation that does not alter the amino acid sequence of the encoded polypeptide even though the nucleotide sequence has changed
beneficial mutation
a mutation that has a beneficial effect on phenotype
neutral mutation
a mutation that has no detectable effect on protein function or no detectable effect on the survival of the organism
nonsense mutations
a mutation that involves a change from a sense codon to a stop codon
frameshift mutations
a mutation that involves the addition or deletion of nucleotides not in a multiple of three and thereby shifts the reading frame of the codon sequence downstream from the mutation
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 death of an organism
reversion
a mutation that returns a mutant allele back to the wild-type allele
mutation
a permanent change in the genetic material that can be passed from cell to cell or from parent to offspring
transversion
a point mutation in which a purine is interchanged with a pyrimidine, or vice versa
base substitutions
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)
apurinic site
a site in DNA that is missing a purine base
intergenic suppressor
a suppressor mutation that is in a different gene from the gene that contains the first mutation
intragenic suppressor
a suppressor mutation that is within the same gene as the first mutation that is suppresses
replica plating
a technique in which a replica of bacterial colonies is transferred to a new petri plate
Ames test
a test using strains of a bacterium, Salmonella typhimurium, to determine if a substance is a mutagen
base excision repair
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
photoreactivation
a type of DNA repair of thymine dimers via photolyase that requires light
ethyl methanesulfonate (EMS)
a type of chemical mutagen that alkylates bases (i.e., attaches methyl or ethyl groups)
acridine dyes
a type of chemical mutagen that causes frameshift mutations
proflavin
a type of chemical mutagen that causes frameshift mutations
nitrous acid
a type of chemical mutagen that deaminates bases, thereby changing amino groups to keto groups
dynamic mutation
a type of mutation in which a repeated sequence, such as three nucleotides, can readily increase in number from one generation to the next
trinucleotide repeat expansion (TNRE)
a type of mutation that involves an increase in the number of tandemly repeated trinucleotide sequences
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
mutant alleles
alleles that have been created by altering a wild-type allele by mutation
homologous recombination repair (HRR)
also called homology-directed repair, occurs when the DNA strands from a sister chromatid are used to repair a lesion in the other sister chromatid
mutagens
an agent that causes alterations in the structure of DNA
nitrogen mustard
an alkylating agent that can cause mutations in DNA
photolyase
an enzyme found in yeast and plants that can repair thymine dimers by splitting the dimers, which returns the DNA to its original condition
DNA-N-glycosylase
an enzyme that can recognize an abnormal base and cleave the bond between it and the sugar in the DNA backbone
alkytransferase
an enzyme that can remove methyl or ethyl groups from guanine bases
oxidative stress
an imbalance between the production of reactive oxygen species (ROS) and an organism's ability to break them down
somatic cells
any cell of the body except for germ-line cells that give rise to gametes
oxidative DNA damage
changes in DNA structure that are caused by reactive oxygen species (ROS)
polarity
in genetics, the phenomenon in which a nonsense mutation in one gene affects the translation of a downstream gene in an operon
reactive oxygen species (ROS)
products of oxygen metabolism in all aerobic organisms that can damage cellular molecules, including DNA, proteins, and lipids
hot spots
sites within a gene that are more likely to be mutated than other locations
tautomer
the forms of certain small molecules, such as bases, which can spontaneously interconvert between chemically similar forms
nonhomologous end joining (NHEJ)
the joining of DNA fragment ends that are different
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
nick translation
the phenomenon in which DNA polymerase uses its 5' to 3' exonuclease activity to remove a region of DNA, and at the same time, replaces it with new DNA
anticipation
the phenomenon in which the severity of an inherited disease tends to get worse in future generations
breakpoint
the region where two chromosome pieces break and rejoin with other chromosome pieces
wild type
the relatively prevalent genotype in a natural population
depurination
the removal of a purine base from DNA
deamination
the removal of an amino group from a molecule. For example, the removal of an amino group from cytosine produces uracil
translesion synthesis (TLS)
the synthesis of DNA over a template strand that harbors some type of DNA damage. This occurs via lesion-replicating polymerases
genetic mosaic
when the cells of part of an organism differ genetically from the rest of the organism
base mismatch
when two bases opposite each other in a double helix do not conform to the AT/GC rule. For example, if A were opposite C, that would be a base mismatch