🧪 General Principles🟡 High-yieldGenetics

Types of Mutation

The ways a change in DNA sequence alters the reading of a gene, from a single silent base swap to a whole shifted reading frame.

Key points

Point mutations: silent codes for the same amino acid, missense codes for a different one, nonsense creates a premature stop codon.
Missense may be conservative (chemically similar amino acid) or non-conservative; sickle-cell disease is the classic non-conservative swap of glutamate for valine in beta-globin.
Frameshift means an insertion or deletion that is not a multiple of three bases, so every downstream codon is misread and a premature stop usually follows.
Splice-site mutations disrupt the conserved intron boundaries, producing exon skipping or intron retention; this is one recognised mechanism of beta-thalassaemia.
Trinucleotide repeat expansions explain anticipation: CAG in Huntington disease, CGG in fragile X syndrome, CTG in myotonic dystrophy.

Silent stays the same, Missense is mistaken, Nonsense stops the sense, Frameshift loses the frame.

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🧪 General Principles🟡 High-yieldGenetics

The ways a change in DNA sequence alters the reading of a gene, from a single silent base swap to a whole shifted reading frame.

Point mutations: silent codes for the same amino acid, missense codes for a different one, nonsense creates a premature stop codon.
Missense may be conservative (chemically similar amino acid) or non-conservative; sickle-cell disease is the classic non-conservative swap of glutamate for valine in beta-globin.
Frameshift means an insertion or deletion that is not a multiple of three bases, so every downstream codon is misread and a premature stop usually follows.
Splice-site mutations disrupt the conserved intron boundaries, producing exon skipping or intron retention; this is one recognised mechanism of beta-thalassaemia.
Trinucleotide repeat expansions explain anticipation: CAG in Huntington disease, CGG in fragile X syndrome, CTG in myotonic dystrophy.

Silent stays the same, Missense is mistaken, Nonsense stops the sense, Frameshift loses the frame.