30. Mutation types and definitions Flashcards
What is a mutation defined as?
An alteration in DNA sequence
What are the four categories of mutations?
Germline
Somatic
Spontaneous
Induced
How heritable are germline mutations?
- Germline means cells which give rise to egg/sperm so passed onto foetus
- All cells in the offspring carry the mutation genotype but the phenotype is only in cells/tissues expressing the gene
To what extent are somatic mutations heritable?
Somatic mutations are not heritable as they only affect somatic cell patches that arise from the original cell
How is the time in development that the mutation occurs linked to the size of the mutation patch?
The earlier in development the mutation occurs the bigger the patch
What sort of mutations give rise to cancer?
Most mutations in cancer are somatic, affecting a single cell which can form tumours and spread (metastasis)
What are spontaneous mutations?
Spontaneous “de novo” mutations can occur at every DNA synthesis stage of cell division
How does the size of the gene influence the mutation rate?
If a gene is large it can be more prone to spontaneous mutations
What are induced mutations?
They are caused by environmental mutagens
What are mutagens?
They are physical or chemical agents that increase the rate of genetic material changes (chemicals, radiation, uv light)
What are the four types of chromosomal mutations?
- Deletion
- Duplication
- Inversion
- Translocation
What is the deletion mutation for chromosomes?
The loss of a gene due to a break in the chromosome, deleting the genetic material
What is the duplication mutation in a chromosome?
Causes gene dosage effect in which genetic material is duplicated
Which 2 types of chromosomal mutations change the amount of genetic material present?
Deletion and duplication change the amount of genetic material
What does the inversion mutation involve for chromosomes?
Where there is the rearrangement of genetic material - causing disruption or fusion of genes
What does the translocation mutation involve?
Genetic material relocated and joins another chromosome - rearrangement may cause disruption or fusion of genes
Which two types of mutations do not change the amount of genetic material?
Inversion and first generation translocation
What are the three types of mutations for a single base pair?
Silent
Missense
Nonsense
What is a silent mutation?
Where there is no change in the gene product due to the degeneracy of the code and wobble
What may a missense mutation cause?
Where there is an amino acid substitution in the gene product due to a change in the first second or third base
What is the phenotypic affect of a missense mutation?
Could have very little effect on protein function unless a very important amino acid is lost or the added amino acid changes the 3D protein or binding location
What does a nonsense mutation involve?
Premature termination of translation where a stop codon is encoded for instead
- can have a large effect if it occurs early on and large parts of the protein are then missing
How may amino acid deletion/insertion mutations have an affect?
- If the insertion/deletion is divisible by three then there could be very little effect on protein function unless a very important amino acid is lost or the added amino acid changes the 3D protein structure
- Frameshift if not divisible by three; depending on how early in the sequence this occurs these mutation often have large effects as they change all subsequent amino acids or lead to premature stop codons
