Chapter 13

Question 1

Define mutation:
What are mutations the source of?
What are they useful for?

Answer 1

Inherited alterations in the DNA
sequence.

• Source of all genetic variation, which further provides
  the raw material for evolution
• Source of many diseases and disorders

Useful for probing fundamental biological
processes

Question 2

Somatic mutations:

Answer 2

mutation in a cell that does not
give rise to gametes

Question 3

Germ-line mutations:

Answer 3

mutation in a germ-line cell

Question 4

Somatic vs Germ-line

Answer 4

Germ cells pass on genetic information to the next generation, but somatic cells repair and reproduce only in one body. Somatic cells do not contribute to the creation of offspring, whereas germ cells do. Germ cells go through both meiosis and mitosis, whereas somatic cells only go through mitosis

Question 5

What are the types of genetic mutation?

Answer 5

Base substitution (transition and transversion)

Insertions/deletions (indels)

Frameshift mutations (In-frame insertions and deletions)

Expanding nucleotide repeats

Question 6

What are base substitutions? What is the difference between transition and transversion? What are the possible base changes for each?

Answer 6

Base substitutions are single pair of bases in DNA being altered.

Transitions: Purine to Purine or Pyrimidine to Pyrimidine.
Possible base changes: A to G, G to A; T to C, C to T

Transversions: Purine to Pyrimidine or Pyrimidine to Purine.
Possible base changes: A to C, A to T, G to C, G to T; C to A, C to G, T to A, T to G

Question 7

What are indels? What are the two things that go with it?

Answer 7

A mutation named with the blend of insertion and deletion.

Insertion: An insertion changes the DNA sequence by adding one or more nucleotides to the gene

Deletion: A deletion changes the DNA sequence by removing at least one nucleotide in a gene

Question 8

What are frameshift mutations?

Answer 8

A genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read.
Causes gene’s codes in groups of three to change, either an extra codon or not enough codons

Question 9

What are expanding nucleotide repeats?

Answer 9

An increase in the number of copies of a set of nucleotides. Occurs when the number of triplets present in a mutated gene is greater than the number found in a normal gene

Question 10

What are the ten phenotypic effects of mutations?

Answer 10

Forward mutation
Reverse mutation
Missense mutation
nonsense mutation
silent mutation
neutral mutation
loss-of-function mutation
gain-of-function mutation
conditional mutation
lethal mutation

Question 11

What are forward mutations?
What are reverse mutations?

Answer 11

Wild type to mutant type

Mutant type to wild type

Question 12

What are missense mutations?

Answer 12

Amino acid to different amino acid

Question 13

What are nonsense mutations?

Answer 13

Sense codon to nonsense codon. Makes stop codon

Question 14

What are silent mutations?

Answer 14

Codon to synonymous codon. No change in amino acid sequence

Question 15

What are neutral mutations?

Answer 15

No change in function

Question 16

What are loss-of-function mutations?

Answer 16

Complete or partial absence of normal protein function

Question 17

What are gain-of-function mutations?

Answer 17

Produce a protein or gene product whose function is not normally present.

Question 18

What is a conditional mutation?

Answer 18

Only expressed under certain conditions

Question 19

What are lethal mutations?

Answer 19

Cause premature death

Question 20

What are suppressor mutations?

Answer 20

A mutation that hides or suppresses the effect of another mutation.

Question 21

What are double mutants?

Answer 21

The result of two simultaneous mutations.

Question 22

What are intragenic mutations

Answer 22

Mutation within the same gene location

Question 23

What are intergenic mutations?

Answer 23

Mutation within different location on the gene.

Question 24

What are spontaneous mutations?

Answer 24

Natural changes in DNA structure or from replication error. Chemical changes to DNA

Question 25

What are induced mutations?

Answer 25

Mutations made to happen
Mutations from an environmental agent such as a chemical or radiation

Question 26

What are mutation rates?

What are three things that go with mutation rates?

Answer 26

The frequency with which a wild type allele at a locus changes into a mutant allele.

• Rates of spontaneous mutations are generally low
• Affected by environmental and genetic factors
• Variation in mutation rates between genes and
  species

Question 27

What does the Ames Test do?

Answer 27

Detects mutagens. Test used to see if a product is causes any mutations.

– Both cancer and mutations result from damage to DNA
– 90% of carcinogens are also mutagens
– Use bacteria as an indicator of carcinogenesis in humans

Question 28

What are transposable elements? What kind of mutations may they cause?

Answer 28

Sequences that can move about the genome. May cause mutations (deletions, duplications, and inversions) “jumping genes”

Question 29

What are the features of transposable elements? (Two types of repeats)

Answer 29

Flanking direct repeats: 3-12 bp long

Terminal inverted repeats: 9-40 bp long

Question 30

How do transposable elements effect the genome?

Answer 30

They’re mobile DNA sequences that are capable of inducing mutations.

Question 31

Generally speaking, what does DNA repair require? What is redundancy?

Answer 31

It requires two nucleotide strands of DNA- Template

More than one type of DNA damage can be repaired by more than one pathway of repair

Question 32

What is mismatch repair?

Answer 32

Corrects mismatched nucleotides in DNA after replication

Question 33

What is direct repair?

Answer 33

DNA repair in which modified bases are changed back into their original structures. It requires special enzymes for each type of repair

Question 34

What is base-excision repair?
What do glycosylases do?

Answer 34

DNA repair that first excises modified bases using glycosylases and then replaces the entire nucleotide.

Glycosylases recognize
inappropriately paired
bases and breaks the
bond between the
base and the
deoxyribose group.

Question 35

What is nucleotide-excision repair?
What are the proteins called? How is the cut-out sequence fixed? What seals the nick left by polymerase?

Answer 35

DNA repair that removes bulky DNA lesions and other types of DNA damage.
Proteins: Uvr for UV repair
DNA polymerase I fixes cut-out sequence
DNA ligase seals nicks

Question 36

What are the two types of double strand repair?

(NOT the stuff with repeats)

Answer 36

Non-homologous end joining

Homologous Recombination

Question 37

What does translesion DNA polymerase do?

Answer 37

Enable cells to tolerate many forms of DNA damage

Question 38

What are genetic diseases (2) caused by faulty DNA repair? What do they mean?

Answer 38

Xeroderma pigmentosum: Autosomal recessive condition. Defects in nucleotide-excision repair. Sun sensitivity, leads to skin cancer

Cancer: Mismatch in DNA repair. High incidences of specific cancers (colon cancer, HNPCC)