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