Molecular basis of mutations — A/L Biology

What must I remember about Molecular basis of mutations?

• A mutation is a permanent, heritable alteration in the nucleotide sequence of an organism's genome.
• Point mutations (single base-pair changes): Silent mutations (no amino acid change due to codon degeneracy), Missense mutations (substitutes a different amino acid, e.g., Sickle-cell anemia), and Nonsense mutations (converts a coding triplet into a premature Stop codon).
• Frameshift mutations: Insertions or deletions of nucleotides not in multiples of three alter the downstream translational reading frame, resulting in completely abnormal truncated polypeptides.
• Chromosomal structural aberrations: Deletion (loss of segment), Duplication (repetition), Inversion (180° reversal within chromosome), and Translocation (exchange between non-homologous chromosomes).
• Mutagenic agents: Physical mutagens (UV radiation forming thymine dimers, ionizing radiation: X-rays, gamma rays) and Chemical mutagens (base analogs, alkylating agents, deaminating chemicals).

Test yourself (1 minute)

1. Sickle-cell disease molecular mechanism

   Single base substitution (GAG to GTG in DNA; GAG to GUG in mRNA) replaces hydrophilic Glutamic acid with hydrophobic Valine at position 6 of the hemoglobin β-globin polypeptide chain.

2. Somatic vs Germline mutations

   Somatic mutations occur in non-reproductive cells and cannot be inherited by offspring; Germline mutations occur in gametes and are transmitted to subsequent generations.

3. Aneuploidy vs Polyploidy

   Aneuploidy is the gain or loss of individual chromosomes (2n ± 1, e.g., Trisomy 21 Down syndrome); Polyploidy is the possession of entire extra sets of chromosomes (3n, 4n).

Practise Molecular basis of mutations questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

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Where does Molecular basis of mutations fit in the syllabus?

Year 1 · Term 2