Mutations Flashcards
Define mutation.
A change of the nucleotide sequence
Define Mutagenesis.
The processs of mutation generation
Describe spontaneous deamination
DNA base is spontaneously changed structure by removing an amine. Cytosine becomes Uracil and 5-Methylcytosine becomes Thymine.
After the first replication this incorrect DNA strand is now used as a template. By the second replication this mistake is now “fixed’ in the DNA.
What is a Transposon?
A tranposable element. As specific DNA sequence It’s supernumerary (many copies) It’s contained in a DNA molecule (sits within chromosome) Moves (transposed) as a discrete unit Moves to random sites Ubiquitous (all species have them) May insertion-ally inactivate genes or change gene expression
CAN JUMP IN OR OUT OF SEQUNCES
What effect may the movement of a transposable element cause?
May mean produced protein is active
May mean produced protein is inactive
May activate transcription by jumping into regulatory sequence
May have no-effect as it may enter an intron
What may a mutation cause?
May or may not cause phenotypic change May be “good” or “bad” Source of genome variation Driving force of evolution May cause disease
What is an SNP?
A single nucleotide polymorphism
One nucleotide change
What are the 3 types of SNP?
Anonymous SNP = no known effect
Non-coding SNP= outside a gene
Coding SNP= inside a gene
What is micro mutation?
Small scale mutation, ie on a base level
Deletion, insertion, substitution etc
What is a macro mutation?
A mutation happens on a large scale, eg at the chromosome level. They are also called chromosome abnormalities,
May occur in meiosis.
Give some examples of macro mutations. (Chromosome abnormalities)
Deletion Duplication Inversion Substitution Translocation
How does the non-overlapping triplet code effect mutations?
It means that if a base is added/deleted the whole frame is shifted changing the way the sequence is read.
What is a Transition mutation? (In bases)
Changes to the same type of base
Purine goes to Purine (A and G)
Pyrimidine goes to Pyrimidine (C and T)
What is a transversion mutation? (In bases)
Change to a different type of base
Purine to pyrimidine (A/G to C/T)
Pyrimidine to purine
What may a single nucleotide mutation cause?
Change in the gene product (RNA or polypeptide)
Change the amount of gene product
Change the polypeptide length
No effect
What is a missense mutation?
Changes the amino acid produced
What is a synonymous mutation?
A silent mutation (no effect)
What could cause a change in polypeptide length?
Frameshift mutation Mutation of STOP codon Nonsense mutation (when a normal codon becomes a STOP codon)
What can mutations that effect regulatory sequences do?
Alter promotor activity
Alter translation initiation (AUG)
Prevent mRNA splicing (introns remain)
Reduce mRNA stability
What could deletions in multiples of 3 base pairs do?
May remove some info but the code might still make sense-could still have functional polypeptide
May remove key codon (eg the active site)-so non-functional polypeptide is made
What is an inversion chromosomal mutation?
Part of the chromosome is inverted (swapped top to bottom,flipped over)
What is a substitution chromosomal mutation?
When a loci on both chromosomes swaps
What is a translocation chromosomal mutation?
When a piece of one chromosome leaves and joins another
What is a micro deletion on a chromosome?
When something is deleted but in imaging the bands on the chromosomes don’t appear to change
What is the difference between paracentric and pericentric inversion in chromosomal mutation?
Paracentric they flip over the centromere
Pericentric doesn’t involve the centromere
What is a Robertsonian translocation?
When 2 different chromosomes break at the centromere. Their Q arms fuse. The small P arms are lost as accentric fragments. (2 chromosomes become one). Often due to the small size of the P arms they don’t contain much info so no phenotypic signs appear
What are Isochromosomes?
When 2 arms on a chromosomes fuse and another is lost
What are ring chromosomes?
When the cell tries to fix a break in a chromosome and ends up fusing it into a ring shape.
What are marker chromosomes?
Not real chromosomes.
Extra bits of DNA floating around
What is polyploidy?
A numerical chromomes abnormality.
The person gains a haploid set as well as the normal diploid set. (69 pairs)
Most common cause is polyspermy
Triploidy occurs in 2-3% pregnancies and causes 15% of miscarriages
What is aneuploidy?
The loss or gain of a whole chromosome
Cause by non-disjunction in meiosis
Trisomies (gain of chromosome)-Downs syndrome
Monosomies (loss of chromosomes)-Turner syndrome
What is Mosaicism?
The presence of 2 or more cell lines in an individual (throughout body or tissue specific)
Caused by non-disjunction in mieosis
Why do we use cytogenetic testing to look for abnormalities?
Accurate diagnosis and prognosis of clinical problems
Better clinical management
Asses future reproductive risks
Prenatal diagnosis
Why would you refer someone for cytogenetic tests?
Prenatal diagnosis Birth defect Abnormal sexual development Infertility Recurring foetal loss Leukaemia Solid tumour Prognostic I for for translocations
When considering the consequences for a persons germ line and somatic cell mutations what do “balanced” and “unbalanced” mean?
Balanced-no genetic info lost, no phenotypic change apparent (may still have a mutation but doesn’t cause issue)
Unbalanced-loose major inf0, phenotypic changes
