20.1 Gene mutations Flashcards
What is the difference between a mutation and a gene mutation
A mutation is any change to quantity or structure of DNA in an organism
A gene mutation is a change to one or more nucleotide bases, or arrangement of bases
What is a substitution mutation
A nucleotide in a section of DNA is replaced by another nucleotide with a different base
What are the 3 possible results of a substitution mutation
- This can form a stop codon that marks the end of the polypeptide chain. So this stops production of the polypeptide and final protein will be different.
- Formation of codon for a different amino acid so the polypeptide chain will differ by one amino acid so it can change shape and function differently. Eg active site is no longer complimentary to substrate.
- Formation of a different codon but it still produces the same amino acid as before because the DNA code is degenerate. So mutation will have no effect on polypeptide chain
What is a deletion mutation
Why is this dangerous
The loss of a nucleotide base from DNA
It results in a frameshift so gene is read in the wrong 3 base groups and the coded information is altered.
Most triplets will be different and the amino acids they code for.
Polypeptide is different so protein functions differently and is non functional. This can impact the phenotype
Why does it matter where the deletion mutation occurs in nucleotide chain
If its at the beginning, all the triplets will be changed so will be read differently.
If its towards the end there will be a smaller impact but there can still be consequences.
What is an addition mutation
An extra base is inserted into the sequence which will result in a frameshift so all the sequence of triplets are altered.
However if 3 bases are added, or a multiple of 3, there may not be a frame shift but there will be a new amino acid.
What is duplication mutation
- One or more bases are repeated.
Produces frameshift
Inversion of bases mutation
A group of bases become separated from the DNA sequence and rejoin at the same position but in the reverse order (back to front).
So base sequence of this proportion is reversed.
Translocation of bases mutation
A group of bases become separated from the DNA sequence on one chromosome and become inserted into DNA sequence of a different chromosome.
These can lead to abnormal phenotype eg cancer or reduced fertility.
What are spontaneous mutations
They are permanent changes in DNA that occur without any outside influence.
They may arise randomly during DNA replication
What are mutagenic agents
Give two examples
Outside factors that increase the basic mutation rate
High energy ionising radiation: Alpha and Beta particles as well as short wavelength radiation eg xrays or uv.
Chemicals eg nitrogen dioxide can interfere with transcription
What is a benefit of mutation
They cause genetic variation which is vital for natural selection and speciation
What is a cost of a mutation
They’re usually harmful and produce an organism which is less suited for its environment.
If mutations occur in body cells rather than gametes this can stop cell division or cause cancer
