Gene Mutation, DNA repair, and Homologous Recombination

Question 1

what provides the raw material for evolution

Answer 1

genetic variation among individuals

Question 2

DNA sequence polymorphism vs. mutations

Answer 2

Mutations: rare(<1% in pop), causes disease or disorder

Polymorphisms: more common(>1% in pop), usually neutral

Question 3

4 different mutation categories and what they’re caused by

Answer 3

Spontaneous: happen naturally and randomly
Induced: Result from extraneous factor
Somatic: don’t occur in germ cells and are not heritable
Germ-line: occur in gametes(heritable)

Question 4

what is a point mutation

Answer 4

a change of one base pair into another in a DNA molecule

Question 5

missense mutation

Answer 5

base pair change that results in an AA change in the protein

Question 6

silent(synonymous mutation)

Answer 6

point mutation that does not alter the AA chain

Question 6

nonsense mutation

Answer 6

a base pair change that creates a stop codon rather than an AA codon

Question 7

what are the two base pair mutations

Answer 7

Transition: purine replaces purine, or pyrimidine replaces pyrimidine
Transversion: pyrimidine replaces purine and vice versa

Question 8

types of frameshift mutations and their consequences

Answer 8

insertion or deletion
-possibly cause
*premature stop codon
*nonsensical AA sequence
*excessively long

Question 9

point mutations vs frameshift mutations

Answer 9

point: replaces one base with another
Frameshift: shortens or lengthens AA chain

Question 10

3 regulatory mutations

Answer 10

promoter
Splicing
Cryptic splicing

Question 11

promoter mutation

Answer 11

alter promoter sequences which interferes with transcription initiation

Question 12

splicing mutation

Answer 12

prevent efficient splicing of introns

Question 13

Cryptic splicing

Answer 13

base-pair substitution that produce new splice sites

Question 14

2 types of functional effects on alleles

Answer 14

loss of function
gain of function

Question 15

examples of loss and gain of function mutations

Answer 15

Loss: Tay-Sachs and double muscling

Gain: Huntingtons and Philadelphia chromosome

Question 16

what is a neutral mutation

Answer 16

mutation in non coding regions

Question 17

what causes slippage

Answer 17

DNA polymerase temporarily disassociates and a portion of newly replicated DNA forms a temporary hairpin

Question 18

what do trinucleotide repeat expansion disorders come from?
how does it correlate to threshold repeat ranges?

Answer 18

arise from strand slippage
if repeats increase beyond threshold it causes the disorder

Question 19

incorporated vs replicated errors

Answer 19

Incorporated: G-T or A-C pairing
Replicated: replication of the incorporated error(initial A-T becomes C-G after replication)

Question 20

depurination vs deamination

Answer 20

Depurination: loss of purine through breaking covalent bond to sugar
Deamination: loss of amino group from a nucleotide base

Question 21

what is an apurinic site

Answer 21

site caused by depurination

Question 22

how can DNA polymerase compensate for an apurinic site

Answer 22

placing an adenine into the site during replication

Question 23

what is the most common cause of spontaneous mutations

Answer 23

base damage from depurination or deamination

Question 24

what is a mutagen

Answer 24

natural or artificial agents that induce mutations

Question 25

mutagen modes of action

Answer 25

nucleotide base analogs deaminating agents alkylating agents oxidizing agents hydroxylating agents intercalating agents

Question 26

what chemical mutagen is common for genetic screens

Answer 26

EMS

Question 27

what is DNA nicking caused by? what can it lead to if not repaired?

Answer 27

distortion of DNA from intercalating agents can cause frameshift mutations

Question 28

T/F nucleotides can be added or lost from DNA nicking

Answer 28

TRUE

Question 29

what is a photoproduct

Answer 29

aberrant structures with additional bonds involving nucleotides due to UV irradiation

Question 30

2 common photoproducts

Answer 30

Thymine dimer: covalent bond between 5 and 6 carbons of adjacent thymines 6-4 photoproduct: covalent bond between carbon 6 of one thymine and carbon 4 of another

Question 31

T/F disruption of replication is the primary cause for the strong association between UV exposure and skin cancer

Answer 31

TRUE

Question 32

differences in what gene leads to diversity in dog sizes

Answer 32

IGF1

Question 33

a missense mutation in what gene leads to the size of Shetland ponies

Answer 33

aggrecan gene

Question 34

what gene and type of mutation causes hairless dogs

Answer 34

7-basepair duplication within exon 1 produces a stop codon(nonsense mutation)

Question 35

main principles of proofreading-mismatch repair

Answer 35

Proofreading: immediately after replication to find mistakes Mismatch: after proofreading, cuts out mistake and replaces it with correct base

Question 36

principles of excision repair

Answer 36

-endonucleases: cut error from strand -DNA polymerase: fills gap with nucleotides -DNA ligase: seals gap at 3' OH end

Question 37

T/F photoactivation repair occurs in humans

Answer 37

FALS

Question 38

how does base excision repair occur? what is the role of nick translation?

Answer 38

repair or replace a damaged or incorrect base -DNA glycosylases recognize and remove base creating an AP site which creates a single stranded nick -DNA polymerase removes area around nick which is filled in by nick translation

Question 39

what genes are involved in NER

Answer 39

uvrA, uvrB, uvrC, and uvrD

Question 40

how does sister chromatid exchange occur? can it lead to mutations?

Answer 40

repair of double-stranded breaks yes it can cause mutations

Question 41

what mechanisms/processes fix out DSBs

Answer 41

NHEJ homologous recombination repair

Question 42

when do DSBs occur

Answer 42

S phase of mitosis

Question 43

what causes bloom's syndrome

Answer 43

mutation in DNA helicase BLM gene

Question 44

what plant was used to study SCE? what mutagens were used to create the SCE?

Answer 44

Barley Maleic acid hydrazide(MH) was used

Question 45

what kind of gain of function mutation was EOE? what gene was it on?

Answer 45

neomorphic stat1

Question 46

what are regulatory mutations

Answer 46

mutations that affect regions such as promoters, introns, and coding for 5' and 3' UTR segments

Question 47

steps of NHEJ

Answer 47

-Ku80 protein complex binds DNA ends -ends are trimmed causing loss of nucleotides -DNA ligase ligates blunt ends to reform an intact duplex

Question 48

steps of homologous recombination repair

Answer 48

-nucleases digest a portion of broken strands, Rad51 binds undamaged chromatid -replication fork assembles on D loop of sister chromatid -new strand synthesis occurs using intact sister strand as template -partial strand excision occurs, duplexes reform, strands are ligated