1.6 Mutations Flashcards
describe ‘the term mutations’
A mutation is a change in the DNA that can result in no protein or an altered protein being expressed.
Mutations occur rarely and randomly under normal circumstances.
what is a gene mutation?
A gene mutation is a change in the sequence nucleotides (bases) in an organisms DNA.
Gene mutations are caused by mistakes during DNA replication.
describe ‘the 3 types of single gene mutations’
Substitution (point mutation)
- one nucleotide is changed for a different nucleotide
- only affects one codon (so one amino acid)
- may or may not affect the final protein produced
Insertion (frameshift mutation)
- a nucleotide is added
- all codons (so all amino acids) from the point of mutation are affected
- protein produced will be different and may not function or may not function properly
Deletion (frameshift mutation)
- a nucleotide is removed
- all codons (so all amino acids) from the point of mutation are affected
- proteins produced will be different and may not function or may not function properly
why is substitution known as a ‘point mutation’ but insertion and deletion known as ‘frameshift mutations’?
substitution only affects one amino acid but insertion and deletion move the ‘reading frame’ and all codons from the point of mutation will be affected
describe ‘the 3 impacts of point mutations’
Missense
- one amino acid is changed for another (MIStake)
- may result in a non-functional protein or have little effect on the protein
Nonsense
- results in a premature stop codon being produced
- results in a shorter protein
Silent
- the change in code creates a code that gives the same amino acid on translation
- protein unaffected
explain ‘how a mutation in a splice site could affect the protein produced’
A mutation at a splice site could result in some introns being retained and/or some exons not being included in the mature transcript. A different mature transcript would lead to the production of a different protein.
what are chromosome mutations?
chromosome mutations are alterations to the structure of one or more chromosomes resulting in a change in the number, sequence or location of genes
describe ‘the 4 types of chromosome mutations’
Duplication
- a section of a chromosome is added from its homologous (matching) partner
- leads to there being more than one copy of some genes on that chromosome
- can be harmful (e.g. cancer genes) or beneficial (e.g. for evolution)
Inversion
- a section of a chromosome is reversed (order of genes is changed)
- can lead to the production of non-viable gametes due to problems in the pairing of chromosomes during gamete formation
Translocation
- a section of a chromosome is added to another non-homologous chromosome
- can lead to the production of non-viable gametes due to problems in the pairing of chromosomes during gamete formation
Deletion
- a section of a chromosome is removed
- these proteins the genes code for will not be produced, which can have a huge impact on the organism
which chromosome mutation is unlikely to produce a normal individual and which are likely to produce a normal individual and why?
duplication, insertion and translocation will present a normal individual as all genes are present
deletion is unlikely to present a normal individual due to genes being missing
how is evolution liked to mutations?
Gene mutations are the only source of new variation in a population. They result in the production of new alleles. Variation provides the raw material for natural selection during evolution.
Duplication allows potential beneficial mutations to occur in a duplicated gene whilst the original gene can still be expressed to produce its protein. Gene duplication is believed to be a major source of new alleles for evolution.
