1. DNA and mutations
SC.912.L.16.4

2. Mutations Alterations in DNA sequence
Some are part of normal DNA variation
Caused by chemical and physiological agents
and errors in DNA replication
Cells can repair some mistakes
If not repaired, changes in DNA sequence
are made permanent by DNA replication

3. Point mutations: Single base mutations:
1. Missense mutation: leads to an amino acid change
2. Silent mutation: does not change the amino acid (NO PHENOTYPIC CHANGE!)
3. Nonsense mutation: causes premature stop-codon

4. Frameshift mutations:
insertion/deletion
duplication
translocation
Altered reading frame
Severe impacts on protein structure-will see a phentotypic change, or potentially lethal

5. Effects of mutations Insignificant (no phenotypic change)
1) Some nucleotide substitution mutations
2) Degeneracy of codons
a) More than one codon for most amino acids
b) Third nucleotide position is often not important e.g., G-U-n = valine; U-C-n = serine; C-G-n = arginine
3) Functional equivalency of amino acids
As long as the amino acid can still function as it is supposed to, there will most often be no phenotypic change

6. Effects of mutations Harmful 1) Some nucleotide substitutions
2) Nucleotide insertions or deletions result in frameshifts, null mutations
3) Altered or lost protein function
If the amino acid and/or protein loses function, there will be a phenotypic change, or mutation will be lethal