4.3 Mutations Flashcards
What is a genetic mutation?
A gene mutation is a change in the sequence of base pairs in a DNA molecule causing the formation of a new allele that may result in an altered polypeptide.
Mutations occur …
continuously.
Why do all mutations in the nucleotide sequence of a gene NOT cause a change in the structure of a polypeptide?
- Genetic code is degenerate
- Mutation may occur in introns / a non-coding sequence
What is a mutagenic agent?
A factor that increases the rate of mutations.
What is insertion?
A mutation that occurs when a nucleotide (with a new base) is randomly inserted into the DNA sequence.
- has a knock-on effect
- forwards frameshift
What is deletion?
A mutation that occurs when a nucleotide is randomly deleted from the DNA sequence.
- has a knock-on effect
- backwards frameshift
What is substitution?
A mutation where a base in the DNA sequence is randomly swapped for a different base.
- Does NOT have a knock on effect.
What are the 3 types of substitution mutations?
- Silent
- Nonsense
- Missense
What is a silent mutation?
The mutation does not alter the amino acid sequence of the polypeptide as the genetic code is degenerate.
What is a nonsense mutation?
The mutation creates a premature stop codon causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function. (e.g. cystic fibrosis)
What is a missense mutation?
The mutation alters a single amino acid in the polypeptide chain. (e.g. sickle cell anaemia)
What is a chromosome mutation?
Non-disjunction occurs when chromosomes fail to separate during meiosis, this is spontaneous.
Therefore these gametes have a different chromosome number than the normal haploid number.
What is an example of a chromosome mutation?
Down syndrome (one extra chromosome)
Turner syndrome (one fewer chromosome)
