Mutations Flashcards
What is DNA damage?
A chemical alteration of DNA e.g addition of group to base
-can lead to mutation due to altered base pairing properties if unrepaired
What is a mutation?
A heritable permanent chnage in base sequence of DNA - spontaneous or from DNA damage
Genotype vs Phenotype
Genotype - describes mutation and gene it occurs in- genetic level - cant see
Phenotype - describes effect on organism - see difference
Wild type vs Mutant
Wild type - organism w usual phenotype
Mutant - if usual phenotype has changed
What are the types of mutation?
- Point mutations - single base change
- Mutations outside coding region
- Gross Mutations
What are point mutations classified on?
-Genotype effect - transition (purine replaced by purine or pyrimidine by pyrimidine). transversion (purine replaced by pyrimidine etc)
-Phenotypic effect - silent, missense, nonsense, frameshift mutations
Silent mutation
If change is in non-coding, regulatory or in third poistion of codon
-has no effect on amino acid sequence of protein
-transversion at genotypic level but silent at phenotypic level
-Accumulate in DNA of an organism and known as polymorphisms
-Responsible for diversity among species
What occurs in missense mutations?
A base change that results in an altered amino acid in a protein - can have none to lethal effect
-Occur in first 2 bases of codon
-Neutral mutation if new amino acid has similar propoerties to original amino acid
Example of missense mutation
Sickle cell disease - glutamic acid in the normal sequence is changed to valine
What occurs in nonsense mutation?
Change an amino acid into a stop codon
-Usually in truncated proteins (short) and altered phenotypes
-impact depends on where made stop
e.g Duchenne’s dystrophy - shortedned dystrophin protein
What occurs in frameshift mutations?
Result from insertion or deletion of bases from the DNA sequence
-All codons after this position will be altered - changes open reading frame
-Usually has serious effect on protein and phenotype of organism
Examples of mutations outside coding regions?
Can affect gene expression
-Promotor- increase or decrease rate of trc
-Transcriptional regulator element - alter trc rate
-Splice junction - alter ability to splice mRNA properly
-Intergenic region - unlikely to effect gene expression
Examples of Gross mutations?
Big changes in DNA
-Deletions -loss of part of DNA sequence - single base or longer stretches
-Insertions - extra bases inserted single to more
-Rearrangements - segments of DNA either within or outside a gene exchanging position
What is a germ-line mutation?
-Occurs in egg or sperm cell
-all cells of offspring affected
What is a somatic mutation?
-affect a limited area in body
-effect depends on when in development mutation occurs
-not transmitted to offspring
-mosaic
