Lecture 12 Flashcards
What is a mutation?
Change in the nucleotide sequence
What is mutagenesis?
The process of mutation generation
What is an endogenous source of mutagenesis?
Transposable elements
This is where DNA moves from one chromosome to another or moves within a chromosome.
Can insert itself into a gene and cause mutation
Is mutagenesis always bad?
No
It may cause disease but also a source of genome variation and the driving force of evolution
What is a single nucleotide polymorphism?
Where a single nucleotide in a codon is changed.
Can be anonymous if no known effect
Non-coding if outside a gene or coding if inside a gene
What is a large scale mutation
One involving a chromosome.
Eg deletion Duplication Inversion Substitution Translocation (swapping)
NB
How is DNA read in transcription?
How is mRNA synthesised?
3’ to 5’ by polymerase
5’ to 3’
How is mRNA read in translation?
How is polypeptide synthesised?
5’ to 3’
N to C terminus aka 5’ to 3’
Results in protein right way around- same as its original DNA
What types of single nucleotide changes are there?
Anaonymous
Coding
Non coding
Deletion
Insertion
Substitution
Transversion= purine to pyrimidine Transition= purine to purine etc
What causes sickle cell anaemia?
A base substitution or missense mutation
What’s an SNP that changes amino acid called?
Missense or non-synonymous
What’s an SNP that doesn’t change amino acid
Silent mutation or synonymous
What can an SNP lead to?
Incorrect amino acid but if stop codon mutated can lead to a frameshift mutation
What is a frameshift mutation?
One in which the polypeptide length is changed
What happens if a regulatory sequence gets mutated?
Right recipe but incorrect method
Alter promoter
Alter initiation
Prevent splicing
Reduce mRNA stability
What is a robertsonian translocation?
P and q arms break apart. P arms lost and Q arms join together. Usually little problem as p arms have little coding material usually. Causes problems later with meiosis as have one chromosome less
What is polyploidy and what is its most common cause?
Extra haploid set of chromosomes. Usually caused by one egg and two sperms
What causes aneuploidy?
Non-disjunction in meiosis
Get trisomies and monosomies.
Trisomy and monosomy happens in all chromosomes but only seen in those viable with life. Eg an extra chromosome 2 in down syndrome
What is cytogenetic testing?
Examining chromosomes to look for structural abnormalities
Chromosomal abnormallities can be balanced or unbalanced, explain?
Balanced= no phenotypic changes (non coding DNA)
Unbalanced= changes (coding DNA)
What is a reciprocal translocation?
Exchange of material between non homologous chromosomes
What is a Robertsonian translocation?
P arms lost and new chromosome formed acts as one chromosome. Problem with meiosis as only 45 chromosomes but usually no problem for individual as P arms have little genetic information.
Great aneuploidy risk for offspring. Can get balanced, monosomy or trisomy
What is the difference between a missense and nonsense mutation?
Missense= SNP resulting in incorrect amino acid
Nonsense= SNP leading to stop codon
