Lecture 4 - Mutations

Question 1

What can mutation be defined as?

Answer 1

Changes to the genetic material that are passed onto the progeny.

Question 2

What are 3 sources of mutation?

Answer 2

• Errors in DNA replication
• Errors in segregating DNA to the daughter cells
• Modification of the genome by other processes, e.g. transposition, DNA damage.

Question 3

What is a substitution?

Answer 3

The replacement of one allele with another.

Question 4

What is a deletion?

Answer 4

The removal of one or more nucleotide from a sequence.

Question 5

What is an insertion?

Answer 5

The addition of one or more nucleotide to a sequence

Question 6

What is recombination?

Answer 6

• Crossing over

- Gene conversion

Question 7

What are inversions?

Answer 7

Flipping 180 of a double-stranded DNA segment.

Question 8

Is polyploidy most often seen in vertebrates or non-vertebrates?

Answer 8

Non-vertebrates

Question 9

Describe the genome of some salmonids.

Answer 9

• Have a partially duplicated genome

- Partially tetraploid

Question 10

What percentage of plants are polyploid?

Answer 10

30-80%

Question 11

What percentage of nucleotides are found in a common form?

Answer 11

99%

Question 12

What are the two common forms of nucleotides?

Answer 12

• Keto; Gs and Ts

- Amino; As and Cs

Question 13

What is the name of a nucleotide that does not exist in its common form?

Answer 13

An isoform, or a tautomer

Question 14

What is a transition?

Answer 14

The exchange of a purine with a purine.

Question 15

What is a purine?

Answer 15

Larger bases: adenine and guanine

Question 16

What is a transversion?

Answer 16

The exchange of a purine with a pyrimidine.q

Question 17

What is a pyrimidine?

Answer 17

Smaller bases: thymine and cytosine.

Question 18

Are there more transitions or transversions?

Why?

Answer 18

Transitions.

Cause less disruption in the DNA helix during synthesis, so less likely to be recognised and corrected.

Question 19

What is spontaneous deamination?

Answer 19

Methylated cytosines spontaneously deaminate to become thymines.

Question 20

How does UV exposure affect base pairing?

Answer 20

• Leads to formation of different bonds between pyrimidines

- Leads to the formation of covalent bonds between adjacent pyrimidines

Question 21

How many replication errors are there in a typical mammalian cell per division?

Answer 21

100,000

Question 22

Describe three DNA repair mechanisms.

Answer 22

• Nicks repaired by DNA ligases
• UV-induced covalent bonds between pyrimidines broken down by photolyase enzymes
• Incorrect bases can be excised and replaced by the mechanism of base excision repair.

Question 23

What is a mutation rate?

Answer 23

The number of mutations per cell division per generation or per unit time.

Question 24

What two adjacent bases have the highest mutation rate in mammalian genomes?

Answer 24

Cytosines next to guanines.

Question 25

What four factors are mutation rates affected by?

Answer 25

• Proximity to the origin of replication
• Repetitive DNA
• Transposable elements
• Telomeres and centromeres

Question 26

Describe the work of Ossowski et al.

Answer 26

• Grew lines of mustard relative plant from single common ancestor over 30 generations.
• Searched for differences to genome of the original ancestor.
• 99 base pair substitutions and 17 insertions.

Question 27

Describe the work of Peris et al (2010).

Answer 27

• Created 100 bacteriophage F1 viruses with random point mutations.
• Measured the fitness of the mutants vs the ancestral strain
• 21% lethal, 35% deleterious, 39% neutral, 2% beneficial.

Question 28

What happened to nematode worms sheltered from selection?

Answer 28

Percentage surviving maturity drops from 98% to 86%

Question 29

what does comparison of sequence divergence between elements of human and mouse genomes show?

Answer 29

That

• Changes at degenerate sites outnumber those at non-generate sites.
• Changes in pseudogenes match the rate of change at degenerate sites.