Genetics Exam 4

mutation rate

- probability that a gene will be altered by a new mutation - gene per cell generation

down mutations

decrease expression

nonionizing radiation

has less energy - cannot penetrate deeply into biological

mutation

heritable change in the genetic material

oxidative stress

imbalance b/t the production of ROS and an organism's ability to break them down

up mutation

increase expression

heterochromatic region

lacks genes

somatic mutation

none of the gametes will carry the mutation

guanine is commonly

oxidized to 8 oxoguanine

reactive oxygen species

oxygen-containing chemical that may react with cellular molecules in a way that may cause harm to DNA.

gene mutations

relatively small change i DNA structure that affects a single gene

deamination

removal of an amino group from the cytosine base

somatic mutations

those that occur directly in a body cell, or in one of its precursor cells

germ line mutations

those that occur directly in a sperm or egg cell, or in one of their precursor cells

NER

- UvA/UvRb complex: recognizes damaged DNA - UvrC (endonuclease) & UvrD (helicase): proteins that act to remove the damaged DNA

trinucleotide repeat expansion

- a repeated seuqence of 3 nucleotide base increases in number generation - typically contain long tracts of glutamine

conditional mutations

- affect the phenotype only under a defined set of conditions - temp-sensitive mutation

mutagens

- agents that are known to alter DNA structure - can be chemcial or physical agents

Lederbergs' replica plating experiment

- bacteria mutate randomly prior to exposure to viruses - bacterial colonies appeared at the same location on each of the two secondary plates

ionizing radiation can cause

- base deltions - oxidized bases - single nicks in DNA strands - cross linking - chromosomal breaks

induced mutations

- caused by environmental agents -mutagens

point mutation

- change in a single base pair - can involve a base substitution

reverse mutation

- changes a mutant allele back to the wild type - reversion

non-ionizing radiation

- contains low energy and long wavelength - includes UV light

deleterious mutation

- decrease the changes of survival - most extreme are lethal mutations

trinucleotide repeat expansion disorders

- fragile x syndrome - myotonic muscular dystrophy - huntington disease

alternative possibility - random mutations

- genetic variation occurs by chance - natural selection results in better adapted organisms

ionizing radiation

- high energy - x rays and gamma rays

phyiscal mutations

- include radiation - X rays, gamma rays, UV light

base analogues

- incorporate into DNA and disrupt structure - some tautomerize at high rates

free radicals

- ionizing radiation produces these chemcially reactive molecules - are mutagenic because they alter the structure of DNA

two common reasons for position effect

- movement to a position next to regulatory sequences - movement to a heterochromatic region

examples of mutations

- nitrous acid - nitrogen mustard - 5-promouracil -2-aminopurine

why is the public concerned about mutagens?

- often involved in development of human cancers - can cause gene mutations that may have harmful effects in future generations

germ line mutation

- one that occurs in a sperm or egg cell - half of gametes will carry mutation

depurination

- removal of a purine from the DNA - covalent bond b/t deoxyribose and a purine base is somewhat unstable

base modifiers

- some covalently modify base structure - others disrupt pairing by alkylating bases

nonsense mutations

- those base substitutions that change a normal codon to a stop codon - results in a premature termination

base excision repair

- used for abnormal bases - N-glycolysase - AP endonuclease - flap endonuclease

genetic mosaic

An individual who has somatic regions that are genotypically different from each other

somatic cells

Any cells in the body other than reproductive cells

Jean baptiste Lamarck - physiological adaptation

Proposed that physiological events (e.g. use and disuse) determine whether traits are passed along to offspring

nonionizing radiaiton includes

UV light

position effect

a gene's expression is changed due to its new location near regulatory seuqences

apurinic site

a site in DNA that is missing a purine base

MutL

acts as a linker that helps loop the DNA

base pair mismatch

addition of a nucleotide that does not obey the AT/GC rule of base pairing

frameshift mutations

addition or deletion of a number of nucleotides that is not divisible by 3

replica plating

bacterial colones are transferred form one plate to another with a sterile piece of velvet cloth

types of frameshift mutations

base deletion/addition

chemical mutagen types

base modifiers, intercalating agents, base analogues

missense mutations

base substitutions that lead to a change in the encoded amino acid

base analogs

become incorporated into daughter strands during DNA replication

base analogs induce mutations by

being incorporated instead of normal bases during DNA replication

nucleotide excision repair fixes

bulky, helix distorting lesions

up promoter mutation

cause the promoter sequence to be more like the consensus sequence

germ line cells

cells that give rise to gametes such as eggs and sperm

transition

change of a pyrimidine (C to T) to another pyrimidine or a purine to another purine

transversion

change of a pyrimidine to a purine or vice versa (T to G)

genome mutations

changes in chromosome number

chromosome mutations

changes in chromosome structure

forward mutation

changes the wild-type genotype into some new variation

euchromatic region

contains functional genes

Which of the bases is most readily deaminated

cytosine

down promoter mutation

decrease the affinity of transcription factors to the promoter

most common spontaneous mutation

depurination

causes of spontaneous mutation

depurination, deamination, tautomeric shift

dna repair system

detection --> removal --> replication

MutS

detects the mismatch

exonucleae

digests the nonmethylated strand

intercalating agents

directly interfere with replication process

alkylating agents cause mutations by

disrupting the normal pairing between nucleotides within the DNA

beneficial mutations

enhance the survival or reproduction success of an organism

photolysase

enzyme that can recognized thymine dimers and split them

how does ionizing radiation cause mutations

forms free radicals that can introduce. breaks into the DNA molecule

genetic anticipation

increase in severity of the symptoms as a disease is passed through future generations

acridine dyes induce mutations by

inserting themselves between adjacent bases and thus distorting DNA structure - frameshift mutation

MutH

makes a cut in a nonmethylated strand - distinguishes b/t the parental strand and the newly made daughter strand

5' UTR/3' UTR

may alter the ability of mRNA to be translated; may alter mRNA stability

splice recognition sequence

may alter the ability of pre-mRNA to be properly spliced

regulatory element/operator site

may disrupt the ability of the gene to be properly regulated

promoter

may increase or decrease the rate of transcription

nitrous acid cause mutations by

modifying bases and thus altering their normal base-pairing properties

random mutation hypothesis

mutations can occur in any gene and do not require the exposure of an organism to an environmental condition or agent

mutation frequency

number of mutant genes divided by the total number of copies of that gene within a population

physical adaptation theory

predicts that the number of ton^r bacteria is very low unless there is a selection, when the numbers created will increase

random mutation theory

predicts that the number of tonr bacteria will fluctuate in different bacterial populations and will occur without selection.

reactive oxygen species (ROS)

products of oxygen metabolism that are produced in all aerobic organisms and that can, if they accumulate, damage cellular molecules, including DNA, proteins, and lipids

spontaneous mutations

results from abnormalities in cellular/biological proceses - underlying cause originates within the cell - ex. errors in dna replication

MutU

separates strands at the cleavage site - NOT involved in mistmatch repair systems

tautomeric shifts

temporary change in base structure

tautomeric shift

temporary change in base structure due to movement of hydrogen atoms

deleterious or beneficial mutations are affected by

the environment

physiological adaptation hypothesis

the resistance of bacteria to T1 infection should arise as a result of exposure to a T1 phage but not before

trinucleotide repeat expansion (TNRE)

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

silent mutations

those base substitutions that do not alter the amino acid sequence of the polypeptide

the base cytosine is deaminated to produce the base

uracil

thymine dimers are typically caused by

uv light

ionizing radiation includes

x rays and gamma rays