01Kinds of mutations
Substitutions: silent (same amino acid), missense (different amino acid — sickle-cell), nonsense (premature stop codon).
Insertions/deletions not in multiples of 3 cause frameshifts, scrambling every codon after them — usually severe.
Causes: replication errors, mutagens (UV light, chemicals, radiation), viruses.
02Mutations and variation
Mutations are the only original source of new alleles. Most are neutral or harmful; a few help. In bacteria, horizontal gene transfer (transformation, transduction, conjugation) also spreads genes, e.g., antibiotic resistance.
Errors in meiosis cause chromosome-level mutations (see 5.6).
03Notebook box
Severity (usually): silent < missense < nonsense ≈ frameshift.
Worked example: Deleting one base near the start codon vs. near the stop codon — which is worse? → Near the start, since more codons downstream are shifted.