mutation - lecture 9 Flashcards
What happens in somatic mutations?
Passed onto new somatic cells via mitosis
What happens in germ - line mutations?
Mutations passed on to approx half members on the next generations
what is a transition mutation?
Change from a purine to a purine or pyrimidine to pyrimidine
what is a transversion mutation?
change from a purine to a pyrimidine or vica versa
How do point mutations occur?
- DNA strands separate for replication
- T base pairs with G. Leading to wobble, an incorporated error
- At the next round G pairs with C , leading to mutation
Depurination
Loss of a purine base, produces an apurinic site.
The apurinic site cannot provide a template for a complementary base. Incorrect nucleotide synthesized
The side effects of depurination
Nucleotide with incorrect base incorporated
Deamination
loss of an amino group
The effects of deamination
can convert bases into one another
What can UV radiation do?
Form a pyrimidine dimer: two thymine bases block replication
strand slippage - what happens when the newly synthesised strand loops out?
Addition of one nucleotide on the new strand
strand slippage - what happens when the template strand loops out?
omission of one nucleotide on the new strand
What happens when homologous chromosomes cross over unequally?
One crossover has insert and other has deletion
What is fragile X?
FMR1 gene - CGG repeat expansion
What does Fragile X lead to?
- learning disabilities
- cognitive impairment
- males more affected
What is the repeat expansion mechanism?
A hair pin forms on the newly synthesised strand . Causes part of the template to be replicated
Why is male mutation rate higher?
male germ line replicates more constantly
Mutation rates
higher for species with small genomes
forward mutation definition
wild type to mutant
reverse mutation definition
mutant type to wild type
missense mutation
new wrong codon encodes incorrect amino acid
nonsense mutation
new codon is a stop codon , premature termination of translation
silent mutation
new codon encodes same amino acid
Intragenic suppressor mutation
- missense muation alters a codon
- second mutation at different site in the same gene may restore the original amino acid
Intergenic suppressor mutation
Base sub at site in another gene, which encodes tRNA, alters the anticodon or the RNA. Can pair with the mutation and incorporated into the sequence
