Mutations

Question 1

What are mutations?

Answer 1

Heritable changes in the base pair sequence of DNA

Question 2

What is a forward mutation?

Answer 2

Changes wild-type allele to a different allele

Question 3

What is a reverse mutation/reversion?

Answer 3

Changes a mutant allele back to wild-type

Question 4

What is a substitution?

Answer 4

Replacement of a base by another base

Question 5

What is a deletion?

Answer 5

Block of one or more bp lost from DNA

Question 6

What is an insertion?

Answer 6

Block of one or more bp added to DNA

Question 7

What is a point/base mutation?

Answer 7

Change from one base pair to another

Question 8

What is a missense mutation?

Answer 8

Results in new triplet code for different AA

Question 9

What is a nonsense mutation?

Answer 9

Results in triplet code for stop codon

Question 10

WHat is a silent mutation?

Answer 10

New triplet code still codes for the same AA

Question 11

What is a neutral mutation?

Answer 11

Mutation in noncoding region

Question 12

What is a transition mutation?

Answer 12

Pyrimidine replaces pyrimidine or purine replaces purine

Question 13

What is a transversion?

Answer 13

Purine and pyrimidine are interchanged

Question 14

What causes frameshift mutations?

Answer 14

Insertions or deletions of nucleotide(s)

Question 15

What is the effect of the addition or loss of a nucleotide?

Answer 15

Shift in reading frame

Question 16

What is a loss-of-function mutation?

Answer 16

Reduces/eliminates function of gene product

Question 17

What is a null mutation?

Answer 17

Results in complete loss of function

Question 18

What is a dominant mutation?

Answer 18

Results in mutant phenotype in diploid organism

Question 19

What is a recessive mutation?

Answer 19

Loss of function

Question 20

What is a dominant negative mutation?

Answer 20

One allele may encode inactive gene product - interferes with function

Question 21

What can cause dominant negative mutation?

Answer 21

Haploinsufficiency

Question 22

What are gain-of-function mutations

Answer 22

Result in a gene product with enhanced, negative or new functions

Question 23

Are gain-of-function mutations usually dominant or recessive?

Answer 23

Dominant

Question 24

What is a suppressor mutation?

Answer 24

Second mutation that reverts or relieves effects of a previous mutation

Question 25

What are somatic mutations?

Answer 25

Occur in any cell except germ cells

Question 26

Are somatic cells heritable?

Answer 26

No

Question 27

What are germ-line mutations?

Answer 27

Occur in gametes

Question 28

Are germ-line mutations inherited?

Answer 28

Yes

Question 29

What are autosomal mutations?

Answer 29

Occur within genes located on autosomes

Question 30

What are X-linked and Y-linked mutations?

Answer 30

Occur within genes located on X and Y chromosome

Question 31

Why is the average mutation rate in gamete-producing eukaryotes higher than that of prokaryotes?

Answer 31

Many cell divisions take place between zygote formation and meiosis in germ cells. More chance for mutation accumulaiton

Question 32

How many mutations does each child contain?

Answer 32

About 60

Question 33

What is the mutation rate in sperm?

Answer 33

2^-4E-8

Question 34

Are mutations more common in sperm from older or younger fathers?

Answer 34

Older

Question 35

Are revertants or forward mutations more rare? Why?

Answer 35

Revertants. Many mutations disrupt gene function, only a few restore function

Question 36

What is depurination?

Answer 36

Hydrolysis of purine base

Question 37

What is deamination?

Answer 37

Removal of an amino (-NH2) group

Question 38

What does deamination cause?

Answer 38

C -> U Normal C-G _> A-T after replication

Question 39

How do cosmic rays and X-rays affect DNA?

Answer 39

Break backbone

Question 40

How does UV light affect DNA?

Answer 40

Forms thymine dimers

Question 41

What is oxidative damage?

Answer 41

8-oxodG mispairs with A

Question 42

What does oxidative damage cause?

Answer 42

Normal G-C -? mutant T-A after replication

Question 43

What is the proofreading portion of DNA called?

Answer 43

3'-to-5' exonuclease

Question 44

How frequently does DNA polymerase incorporate incorrect bases in bacteria and humans?

Answer 44

<10-9

Question 45

What are tautomers?

Answer 45

Similar chemical forms of bases that interconvert regularly

Question 46

Give examples of human disease genes with unstable trinucleotide repeats

Answer 46

Fragile X syndrome Huntington disease

Question 47

What are mutagens?

Answer 47

Agents that cause DNA damage leading to mutations

Question 48

What are the six classifications of chemical mutagens?

Answer 48

Nucleotide base analogs Deaminating agents Alkylating agents Oxidizing agents Hyoxylating agents Intercalating agents

Question 49

How does hydroxylation alter DNA?

Answer 49

Add an -OH group

Question 50

How do alkylating agents affect DNA?

Answer 50

Add ethyl or methyl groups

Question 51

How do intercalators alter DNA?

Answer 51

Insert between bases

Question 52

How does the FDA screen for carcinogens?

Answer 52

Ames test

Question 53

What is an error-prone DNA repair system?

Answer 53

SOS system; microhomology-mediate end-joining (MMEJ(

Question 54

What mechanisms/molecules can reverse DNA base alterations?

Answer 54

Alkyltransferase and photolyase

Question 55

Briefly outline the process of base excision repair

Answer 55

1. DNA glycolyases remove altered nitrogenous base 2. Nearby nucleotides removed 3. New DNA synthesized to fill gap

Question 56

Briefly outline the process of nucleotide excision repair

Answer 56

1. UvrA + UvrB complex scans for distortions to double helix 2. UvrB + UvrC complex cuts around damaged DNA 3. DNA polymerase fills in the gap

Question 57

Why are double-strand breaks harmful for DNA?

Answer 57

Can lead to deletions and chromosome rearrangments if left unrepaired

Question 58

What are the two repair mechanisms for double-strand breaks?

Answer 58

Homologous recombination. non-homolohous end-joinging (NHEJ)

Question 59

How do bacteria use methyl-directed mismatch repaird?

Answer 59

Parental DNA strand marked by adenine methylase where GATC occurs MutS and MutL bind to mismatched nucleotides MutH cuts the unmethylated strand oppositve the methylated GATC Gap made in unmethylated strand by DNA exonucleases Gap filled in by DNA polymerase using the methylated strand as template

Question 60

Why are parental DNA strands methylated in bacteria?

Answer 60

Newly-replicated DNA isn't methylated, helps spot mistakes

Question 61

What causes Xeroderma pigmentosum?

Answer 61

Mutations in any one of secen genes involved in nucleotide excision repair

Question 62

What causes hereditary forms of colorectal cancer?

Answer 62

Mutations in mismatch repair genes

Question 63

What causes hereditary forms of breast cancer?

Answer 63

Mutations of BCRA1 and BCRA2 which are involved in double-strand break repair by homologous recombination