Chapter Seven: Mutations

Question 1

heritable changes in the base pair sequence of DNA

Answer 1

mutations

Question 2

changes wild-type allele to a different allele

Answer 2

forward mutation

Question 3

changes a mutant allele back to wild-type

Answer 3

reverse mutation (reversion)

Question 4

replacement of a base by another base

Answer 4

substitution

Question 5

purine replaced by another purine or pyrimidine replaced by another pyrimidine

Answer 5

transition

Question 6

purine replaced by a pyrimidine

Answer 6

transversion

Question 7

block of one or more base pairs lost from DNA

Answer 7

deletion

Question 8

block of one or more base pairs added to DNA

Answer 8

insertion

Question 9

when both insertion and deletion occur

Answer 9

indel

Question 10

affect one or a few base pairs, altering one gene at a time

Answer 10

point mutations

Question 11

four examples of a point mutation

Answer 11

transitions, transversions, small deletions, small insertions

Question 12

spontaneous mutations occur at a ___

Answer 12

very low rate

Question 13

different ___ have different mutation rates

Answer 13

genes

Question 14

mutation rates depend on ___ and ___

Answer 14

gene size and susceptibility of a gene to mutagens

Question 15

bigger genes are ___ likely to have mutations

Answer 15

more

Question 16

average mutation rate in gamete-producing eukaryotes is ___ than that of prokaryotes

Answer 16

higher

Question 17

why is the mutation rate higher in gamete-producing eukaryotes

Answer 17

many cell divisions take place between zygote formation and meiosis and germ cells, more chances to accumulate mutations

Question 18

human sperm have a ___ mutation rate them human eggs

Answer 18

higher

Question 19

human mutation rate

Answer 19

1x10^-8

Question 20

human mutation rate is estimated by ___

Answer 20

sequencing genomes of parents and their children

Question 21

most mutations do not influence ___

Answer 21

phenotype

Question 22

sperm mutation rate

Answer 22

2^-4x10^-8

Question 23

revertants are more ___ than forward mutations

Answer 23

rare

Question 24

many mutations ___ gene function, only a few ___ gene function

Answer 24

disrupt
restore

Question 25

fluctuation test provided evidence that ___

Answer 25

mutations in bacteria occur spontaneously

Question 26

two hypotheses for the origin of bacterial resistance in the fluctuation test

Answer 26

1. resistance is a physiological response to bactericide 2. resistance arises from random mutation

Question 27

___ verifies that bacterial resistance is the result of preexisting mutations

Answer 27

replica plating

Question 28

bacterial resistance arises from mutations that occurred ___ exposure to bactericide. bactericide becomes a ___.

Answer 28

before selective agent

Question 29

once random mutations occur they usually ___

Answer 29

remain stable

Question 30

base changes are often corrected by ___

Answer 30

DNA repair

Question 31

if a base change does not get corrected before replication, ___

Answer 31

both DNA strands contain the base change and a heritable mutation occurs

Question 32

hydrolysis of a purine base, loss of a purine

Answer 32

depurination

Question 33

removal of an amino group

Answer 33

deamination

Question 34

deamination can change a ___ to a ___

Answer 34

C to a U

Question 35

cosmic rays and x-rays cause DNA damage by ___

Answer 35

breaking the sugar phosphate backbone

Question 36

causes adjacent thymines to form abnormal covalent bonds (thymine dimers)

Answer 36

Ultraviolet rays

Question 37

___ decreases mistakes during replication

Answer 37

proofreading

Question 38

incorporation of incorrect bases by DNA polymerase is __

Answer 38

exceedingly rare

Question 39

proofreading portion of DNA polymerase that recognizes and excises mismatches

Answer 39

3' to 5' exonuclease

Question 40

base tautomerization results in ___

Answer 40

replication mistakes

Question 41

each base has two ___

Answer 41

tautomers

Question 42

addition of 3 nucleotides

Answer 42

expansion

Question 43

deletion of 3 nucleotides

Answer 43

contraction

Question 44

___ and ___ are caused by unstable trinucleotide repeats

Answer 44

fragile X syndrome and Huntington disease

Question 45

expansion and contraction of triplet repeats occurs by ___

Answer 45

slipped mispairing

Question 46

HJ Muller used x-ray dose to ___ in Drosophila

Answer 46

increase mutation rate

Question 47

agents that raise frequency of mutations above spontaneous rate

Answer 47

mutagens

Question 48

chemical structure almost identical to normal base

Answer 48

base analog

Question 49

addition of an OH group

Answer 49

hydroxylation

Question 50

addition of ethyl or methyl groups

Answer 50

alkylation

Question 51

removal of an amine group

Answer 51

deamination

Question 52

insert molecules in between bases

Answer 52

intercalators

Question 53

mutations that occur in non-germ cells

Answer 53

somatic mutations

Question 54

are somatic mutations heritable

Answer 54

no

Question 55

test used to screen for chemicals that cause mutations and therefore might cause cancer

Answer 55

Ames test

Question 56

four accurate DNA repair mechanisms

Answer 56

1. reversal of DNA base alterations 2. homology-dependent repaid of damaged bases or nucleotides 3. double-strand break repair 4. mismatch repair of DNA replication errors

Question 57

two error prone DNA repair systems

Answer 57

1. SOS system 2. microhomology mediated end joining (MMEJ)

Question 58

base excision repair mechanism

Answer 58

1. DNA glycosylases remove altered base 2. AP endonuclease cuts backbone 3. DNA exonuclease removes nucleotides near the cut, creating a gap 4. DNA polymerase synthesizes new DNA to fill the gap 5. DNA ligase seals the cut

Question 59

nucleotide excision repair mechanism

Answer 59

1. UvrA and UvrB scan for distortions to the double helix (thymine dimers for example) 2. UvrB and UvrC endonuclease cut strand containing the distortion 3. damaged fragment is released from DNA 4. DNA polymerase fills in the gap with new DNA 5. DNA ligase seals the cut

Question 60

unrepaired double-strand breaks can lead to ___ and ___

Answer 60

deletions and chromosome rearrangements

Question 61

two repair mechanisms for double-strand breaks

Answer 61

homologous recombination and nonhomologous end-joining

Question 62

in bacteria, ___ corrects mistakes in replication

Answer 62

methyl-directed mismatch repair

Question 63

the SOS system in bacteria is used at ___

Answer 63

replication forks that stalled because of unrepaired DNA damage

Question 64

in the SOS system, DNA polymerase adds ___ opposite damaged bases

Answer 64

random nucleotides

Question 65

xeroderma pigmentosa is caused by ___

Answer 65

mutations in any one of seven genes involved in nucleotide excision repair

Question 66

hereditary forms of colorectal cancer are caused by ___

Answer 66

mutations in mismatch repair genes

Question 67

hereditary forms of breast cancer are caused by ___

Answer 67

BRCA 1 and BRCA 2 involved in double - strand break repair by homologous recombination

Question 68

without ___, life would have died out long ago because it could not have responded to changes int he environment

Answer 68

mutations

Question 69

DNA repair walks a fine line between

Answer 69

being efficient enough to protect genomes and propagation of life