Chapter 15(3)

Question 1

What is a mutation?

Answer 1

a heritable change in DNA sequence

Question 2

What does mutation produce/what is important about mutation?

Answer 2

it produces genetic variation within populations and is the ultimate source of genetic variation for evolution

Question 3

Do spontaneous mutations influencing phenotype occur at a high or low rate?

Answer 3

very low rate

Question 4

Do induced mutations occur at a high or low rate?

Answer 4

can occur at a high rate

Question 5

When do germline mutations occur?

Answer 5

DNA replication in meiosis

Question 6

When do somatic mutations occur?

Answer 6

DNA replication in mitosis

Question 7

What is a point mutation?

Answer 7

mutations that map to a single and specific point (usually a single base pair or a few base pairs)

Question 8

What is a transition mutation?

Answer 8

type of point-mutation where base pair(S) transition from a purine to a purine or a pyrimidine to a pyrimidine

Question 9

What is a transversion mutation?

Answer 9

type of point-mutation where a purine transitions from a purine to a pyrimidine or a pyrimidine to a purine

Question 10

What is an indel mutation?

Answer 10

type of point-mutation that is either an insertion or deletion(we don’t know so we call it an indel)
-can be more than one base pair

Question 11

What is a silent mutation? What is it also called?

Answer 11

type of point-mutation in protein-coding genes where a base pair is changed, but amino acid stays the same
-also called a synonymous mutation

Question 12

What is a missense mutation? What is it also called?

Answer 12

type of point-mutation in a protein coding gene where a base pair is changed, which causes a change in the amino acid
-also called a nonsynonymous mutation

Question 13

What is a nonsense mutation?

Answer 13

type of point-mutation in a protein coding gene where a base pari is altered, causing a new stop codon to be formed

Question 14

What is a frameshift mutation?

Answer 14

type of point-mutation in protein-coding genes where there is an insertion or deletion of a single pair

Question 15

Do all mutations have phenotypic consequences?

Answer 15

No

Question 16

What are spontaneous mutations caused by?

Answer 16

DNA replication errors

Question 17

What are induced mutations?

Answer 17

mutations caused by mutagens

Question 18

What is the result of mutations in regulatory regions?

Answer 18

Every one of these six of these
possible mutations reduces (but
does not eliminate) transcription.
Some promoter mutations can
destroy transcription.

Question 19

What is the approx. mutation rate of DNA replication?

Answer 19

high fidelity with a per bp mutation rate of 1x10^-9

Question 20

What does strand slippage lead to?

Answer 20

strand slippage in regions of repeating DNA sequence leads to an altered number of repeat elements
-daughter strand slippage forms a hairpin loop

Question 21

What kind of mutation are trinucleotide repeat disorders? Example?

Answer 21

spontaneous mutations
-ex: huntington disease

Question 22

What kind of mutation are nucleotide base changes?

Answer 22

spontaneous mutations

Question 23

What are tautomers?

Answer 23

nucleotide base natural alternative forms

Question 24

What is the keto form of a nucleotide?

Answer 24

the dominant form and typical base-pairing of nucleotides

Question 25

What is the enol form of a nucleotide?

Answer 25

less frequent, alternative form of nucleotides that changes the way base-pairing can happen

Question 26

What happens if DNA replication introduces new nucleotides?

Answer 26

causes a mutation

Question 27

What can be the result of base pairing with rare tautomers? What kind of mutation is this?

Answer 27

can induce mutations
-it is a spontaneous mutation

Question 28

What is depurination? What kind of mutation can this lead to?

Answer 28

a spontaneous mutation that results in the loss of a purine
-adenine most commonly incorporated, leading to a transition mutation

Question 29

What is deamination? Where does this commonly occur? What transition takes place?

Answer 29

a spontaneous mutation that results in the removal of an amino group from a base
-most common at cytosine
-A-T–>G-C

Question 30

What is are analogs?

Answer 30

induced mutation- some mutagens act as analogs, which are molecules that mimic nucleotides and can replace them by hydrogen-bonding in a double helix

Question 31

What are Alkylating agent mutagens? What transition takes place?

Answer 31

mutagen that chemically alters the base by adding alkyl groups (methyl or ethyl groups) to positions in the nitrogenous base
-G-C–>A-T

Question 32

What are Ethyl methanosulfate (EMS) mutagens?

Answer 32

mutagen that adds ethyl groups
-when added to oxygen in guanine, it alters base-pairing and can induce transitions

Question 33

What is a hydroxylating mutagen? What transition takes place?

Answer 33

adds hydroxyl groups
-C-G–>T-A

Question 34

Where does slippage most often occur?

Answer 34

in area with repeating nucleotides

Question 35

What kind of mutagen facilitates slippage?

Answer 35

Intercalating mutagens

Question 36

What occurs during Intercalation and what does it cause and result in?

Answer 36

-Intercalation distorts the shape of DNA, causing polymerase to “slip” off (slippage).
-When DNA polymerase starts synthesizing, it may miss a base or add an extra one, causing indels.
-These result in frameshift mutations in protein-coding genes

Question 37

What is Nucleotide Base Excision Repair?

Answer 37

a repair mechanism using the undamaged strand as a template to repair the damaged strand

Question 38

What it it and what does double-stranded breakage lead to?

Answer 38

it is when DNA damage affects both strands, thus one of them cannot be used as a template to repair the other
-this is deadly and/or leads to big chromosomal alterations, and often to cancer

Question 39

What are the two-mechanisms that can repair double-stranded breakage?

Answer 39

1. nonhomologous end joining
2. synthesis-dependent strand annealing

Question 40

What happens during nonhomologous end joining? Is it accurate?

Answer 40

-This mechanism is initiated in G1
prior to DNA synthesis
-Ku80 and Ku70 recognize
broken ends
-Removing the overhanging
nucleotides can induce mutations
with phenotypic consequences if
they occur in protein-coding genes
or regulatory regions

-No, it is error prone

Question 41

How is synthesis-dependent strand annealing initiated and how accurate is it?n

Answer 41

-This mechanism is initiated if DNA
has already been synthesized
-This mechanism is an error-free
repair mechanism