Chapter 7 (book)

Question 1

Mutation

Answer 1

A heritable change in genetic material

Question 2

A mutation that changes a wild-type allele of a gene to a different allele is called a [] mutation

Answer 2

Forward

Question 3

Relationship between a mutant allele and the wild-type allele from which it originated

Answer 3

Mutant alleles can be either recessive or dominant to the original wild-type allele.

Question 4

Consider the following change in a DNA sequence (for simplicity only one of the DNA strands is written): 5’-AATGTGGATG-3’ to 5’-AATGTGCATG-3’. What type of mutation is this?

Answer 4

Base substitution

Question 5

Base change is a transition mutation

Answer 5

A to G or T to C and vice versa

Question 6

Current estimate of the rate of spontaneous mutations in eukaryotic organisms

Answer 6

About 10–6 mutations per gene per gamete

Question 7

Easiest to mutate in a mutant screen

Answer 7

The longest one

Question 8

A mutant allele is best defined as an allele that ______.

Answer 8

has a different DNA sequence from the wild-type

Question 9

Why multicellular organisms have a higher mutation rate than bacteria

Answer 9

Mutations may occur at multiple stages of development before gametes form.

Question 10

A change of one DNA base to one of the other three DNA bases is described as a base ______ mutation.

Answer 10

Substitution

Question 11

Replica plating

Answer 11

a process whereby colonies on a master plate are picked up on velvet and then transferred to media in other petri plates to test for phenotype.

Question 12

A [] is a type of base substitution that involves a change of a pyrimidine to another pyrimidine, or a purine to another purine.

Answer 12

Transition

Question 13

Mechanism by which spontaneous heritable mutations can appear

Answer 13

In order for a heritable mutation to appear, DNA must be altered and replicated before it is repaired.

Question 14

Rate of Spontaneous mutations

Answer 14

Very low

Question 15

Depurinization

Answer 15

The removal of a purine from DNA is called

Question 16

One of the main determinants of the mutation rate of a particular gene.

Answer 16

Length of the coding sequence

Question 17

Rate of spontaneous mutations

Answer 17

Once in 10^9 base pairs.

Question 18

[] have higher mutation rates because many chances exist for mutations to accumulate in germ-line cells.

Answer 18

Multicellular eukaryotes

Question 19

A mouse has a mutation in the DNA polymerase gene that impairs its 3’-to-5’ exonuclease domain. What consequence would you expect?

Answer 19

DNA replication will have a higher error rate. The nuclease portion of the polymerase molecule called the 3’-to-5’ exonuclease recognizes a mispaired base and excises it, allowing the polymerase to copy the nucleotide correctly. Without it the error rate of DNA replication increases.

Question 20

“potential” mutations

Answer 20

When changes in DNA appear. Most of them are repaired before the altered DNA is replicated

Question 21

Why DNA mutations are rare

Answer 21

• When changes in DNA appear, they are initially considered “potential” mutations because most of them are repaired before the altered DNA is replicated
• Even though DNA replication is very accurate, it can introduce errors, typically, less than once in every 10^9 base pairs.
• The polymerase has a 3’-to-5’ exonuclease accounting for the low error rate in DNA replication

Question 22

Tautomerization

Answer 22

temporary change in base structure due to movement of hydrogen atoms.

Question 23

In order for a heritable mutation to appear…

Answer 23

DNA must be altered and replicated before it is repaired.

Question 24

A base tautomerization usually…

Answer 24

leads to a base substitution

Question 25

The equilibrium between tautomer’s, chemical forms interconverting continually...

Answer 25

is such that each base is almost in the form where A pairs with T and G pairs with C. However, if by chance a base in the template strand is in its rare tautomeric form when DNA polymerase arrives, the wrong base will be incorporated into the newly synthesized chain because the rare tautomer’s pair different than the normal forms. If the misincorporated nucleotide is not corrected by mismatch repair before the next round of replication, a point mutation results.

Question 26

Repeated sequences of three bases that can change in number generation after generation are called []

Answer 26

unstable trinucleotide repeats

Question 27

tautomer

Answer 27

A temporary change in the structure of a nitrogen base due to movement of hydrogen atoms is called a(n)

Question 28

Assume thymine was in its rare tautomeric state when DNA polymerase used it as a template during replication. After a second round of replication...

Answer 28

the result would be a TA to CG mutation in one of the four daughter molecules

Question 29

Mutagen

Answer 29

An agent that can change DNA structure and cause mutations.

Question 30

Unstable trinucleotide repeats

Answer 30

Repeated sequences of three bases that can increase or decrease in number generation after generation.

Question 31

base analogs

Answer 31

Certain compounds have a structure similar to normal DNA bases and can be incorporated into daughter strands during DNA replication.

Question 32

Muller Experiment

Answer 32

In his experiments with Drosophila, Muller exposed male flies to increasingly large doses of X-rays and mated them to females that had a Bar-marked Balancer X chromosome. Bar-eyed F1 females carrying a paternal X chromosome with a lethal mutation would produce sons only with Bar eyes

Question 33

Alkylating agents

Answer 33

cause mutations by adding methyl or ethyl groups that disrupt base pairing

Question 34

Deaminating agents

Answer 34

cause mutations by modifying bases and thus altering their normal base-pairing properties. Ex: nitrous acid

Question 35

Base analogs induce mutations

Answer 35

by incorporation into DNA instead of normal bases and tautomerization

Question 36

5-Bromouracil

Answer 36

Is incorporated into DNA instead of thymine, but can pair with guanine

Question 37

Hydroxylamine

Answer 37

. | mutate DNA by adding a –OH group to(from) cytosine, which allows it to pair with adenine.

Question 38

Ethylmethane sulfonate

Answer 38

Adds an ethyl group to guanine, which then pair incorrectly

Question 39

Nitrous acid

Answer 39

Nitrous acid removes a namine, NH2 (deaminates), or amino group from adenine or cytosine, changing the bases to which they can pair. This leads to mutations in the newly-synthesized DNA strand during DNA replication.

Question 40

Proflavin

Answer 40

Intercalates into the double helix between base pairs, causing deletions and insertions

Question 41

polyQ trinucleotide repeat expansion disorders

Answer 41

CAG | Proteins associated with polyQ trinucleotide repeat expansion disorders contain long tracts of the amino acid glutamine

Question 42

Alkylating agents

Answer 42

covalently attach methyl or ethyl groups to DNA bases, and thus disrupt their normal base pairing properties.

Question 43

gain-of-function allele

Answer 43

When a mutant allele specifies a protein with functions qualitatively different from those of the corresponding wild-type protein

Question 44

polyQ diseases

Answer 44

human neurological diseases caused by germ-line expansion of CAG repeats. The CAG repeats are codons specifying a run of glutamine

Question 45

non-polyQ diseases

Answer 45

human single-gene neurological diseases caused by germ-line expansion of trinucleotide repeats. The expanded trinucleotide region affects gene expression although it is outside the open reading frame.

Question 46

mutations in somatic cells are important...

Answer 46

they can affect genes that regulate cell growth and division and therefore cause cancer.

Question 47

In humans, the normal HD+ allele has...

Answer 47

between 6 and 28 CAG repeats

Question 48

Ames test

Answer 48

screen for chemicals that cause mutations in bacterial cells. assays whether a chemical agent causes mutations The Ames test uses a strain of the bacterium Salmonella typhimurium that is unable to produce histidine The organism used in the Ames test is a bacterium

Question 49

Carcinogen

Answer 49

a substance that causes cancer; a mutagen. | Mutagens are sometimes called carcinogens because mutations cause cancer.

Question 50

mutant HD allele

Answer 50

considered a gain-of-function mutant allele

Question 51

Gain of function mutants

Answer 51

specify proteins whose functions are quantitively different from those of the corresponding wild type.

Question 52

Loss of function

Answer 52

prevent protein production

Question 53

expected characteristics of a mutagen that acts as an intercalating agent

Answer 53

it is flat, planar molecule.

Question 54

thymine dimers

Answer 54

covalent linkage between adjacent thymine residues in DNA that can cause mutation

Question 55

Necessities for the cell to enzymatically correct a thymine dimer

Answer 55

Photolyase, chromophore, and light

Question 56

Base excision repair

Answer 56

Relies on enzymes called DNA glycosylases that cleave altered bases from the sugar of their nucleotide. Base excision repair is the main system used in the repair of abnormal bases

Question 57

Nucleotide excision repair (NER)

Answer 57

the main system used in the repair of base alterations that cannot be repaired by base excision

Question 58

Cause of Double-strand breaks in DNA

Answer 58

X-rays

Question 59

photolyase

Answer 59

The enzyme that can recognize thymine dimers and split

Question 60

Alkyltransferase

Answer 60

The enzyme that can remove methyl and ethyl groups from guanine

Question 61

Double-strand breaks are typically repaired by

Answer 61

Nonhomologous end-joining and Homologous recombination repair. The breakage of chromosomes is referred to as a double strand

Question 62

During NHEJ

Answer 62

the two broken ends of DNA are directly attached back together. Non homologous end joining

Question 63

Correction for: During DNA replication, a base that does not obey the normal base pairing rules is added

Answer 63

Corrected by methyl-directed mismatch repair

Question 64

nucleotide excision repair.

Answer 64

Removes altered bases that cannot be recognized by any of the cellular glycosylases

Question 65

SOS system

Answer 65

error-prone DNA repair involving "sloppy" DNA polymerases that are attracted to stalled replication forks, where they insert random nucleotides an emergency repair system in bacteria that relies on error-prone DNA polymerases; these special SOS polymerases allow cells with damaged DNA to divide, but the daughter cells carry many new mutations.

Question 66

The two main mechanisms used to repair DNA double-strand breaks

Answer 66

homologous recombination repair | nonhomologous end-joining.

Question 67

Nucleotide excision repair (NER)

Answer 67

main system used in the repair of base alterations that cannot be repaired by base excision

Question 68

Several forms of cancer associated with defects...

Answer 68

in DNA repair systems. Failure of DNA repair allows mutations to accumulate that can lead to unregulated cell division.