Lecture 4 - Mutations Flashcards
What can mutation be defined as?
Changes to the genetic material that are passed onto the progeny.
What are 3 sources of mutation?
- Errors in DNA replication
- Errors in segregating DNA to the daughter cells
- Modification of the genome by other processes, e.g. transposition, DNA damage.
What is a substitution?
The replacement of one allele with another.
What is a deletion?
The removal of one or more nucleotide from a sequence.
What is an insertion?
The addition of one or more nucleotide to a sequence
What is recombination?
- Crossing over
- Gene conversion
What are inversions?
Flipping 180 of a double-stranded DNA segment.
Is polyploidy most often seen in vertebrates or non-vertebrates?
Non-vertebrates
Describe the genome of some salmonids.
- Have a partially duplicated genome
- Partially tetraploid
What percentage of plants are polyploid?
30-80%
What percentage of nucleotides are found in a common form?
99%
What are the two common forms of nucleotides?
- Keto; Gs and Ts
- Amino; As and Cs
What is the name of a nucleotide that does not exist in its common form?
An isoform, or a tautomer
What is a transition?
The exchange of a purine with a purine.
What is a purine?
Larger bases: adenine and guanine
What is a transversion?
The exchange of a purine with a pyrimidine.q
What is a pyrimidine?
Smaller bases: thymine and cytosine.
Are there more transitions or transversions?
Why?
Transitions.
Cause less disruption in the DNA helix during synthesis, so less likely to be recognised and corrected.
What is spontaneous deamination?
Methylated cytosines spontaneously deaminate to become thymines.
How does UV exposure affect base pairing?
- Leads to formation of different bonds between pyrimidines
- Leads to the formation of covalent bonds between adjacent pyrimidines
How many replication errors are there in a typical mammalian cell per division?
100,000
Describe three DNA repair mechanisms.
- 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.
What is a mutation rate?
The number of mutations per cell division per generation or per unit time.
What two adjacent bases have the highest mutation rate in mammalian genomes?
Cytosines next to guanines.
What four factors are mutation rates affected by?
- Proximity to the origin of replication
- Repetitive DNA
- Transposable elements
- Telomeres and centromeres
Describe the work of Ossowski et al.
- 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.
Describe the work of Peris et al (2010).
- 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.
What happened to nematode worms sheltered from selection?
Percentage surviving maturity drops from 98% to 86%
what does comparison of sequence divergence between elements of human and mouse genomes show?
That
- Changes at degenerate sites outnumber those at non-generate sites.
- Changes in pseudogenes match the rate of change at degenerate sites.
