Biology · MU Pleven

20.Gene mutations. Molecular diseases.

Explains gene mutations as permanent changes in DNA sequence, covering germ-line versus somatic mutations, forward and reverse mutations, and deleterious, lethal and conditional types. It then classifies point mutations (base substitutions such as transitions and transversions, silent, missense, nonsense and frameshift effects), non-coding and trinucleotide repeat expansions, and spontaneous causes like depurination, deamination and tautomeric shift. It closes with sickle cell anaemia, thalassaemia, phenylketonuria and G6PD deficiency, including a mnemonic for tautomeric shifts.

Inside: 11 sections · 3 labelled pictures · 1 formula · 11 flashcards · 4 min

Topic 20 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 11 sections, about 513 words (4 min of reading), with 11 flashcards.

In this note

  1. Gene mutations. Molecular diseases.
  2. GENE MUTATIONS
  3. Genetic Terms
  4. Types of Mutations
  5. Types of Gene Mutation
  6. Point Mutations
  7. Effects of Point Mutations
  8. Mutations in Non‑Coding Sequences
  9. Trinucleotide Repeat Expansion (TNRE)
  10. Causes of Mutation
  11. Human Molecular Diseases Due to Mutation

GENE MUTATIONS

A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. Mutations vary in size, from a single base pair to a large chromosomal segment containing multiple genes.

  • Mutations in reproductive cells can be passed to offspring.
  • They provide allelic variation, the ultimate source of genetic variation and evolutionary change.
  • Phenotypic effects range from neutral, harmful (e.g., haemophilia), to beneficial (e.g., light skin at high latitudes).
  • Haemophilia A: mutation in gene for factor VIII → deficiency.
  • Haemophilia B (Christmas disease): mutation causing factor IX deficiency.
  • Many inherited diseases result from mutated genes.
  • Cancer: Caused when carcinogens induce mutations.
  • Germ-line mutations: Occur in sperm/egg → inherited.
  • Somatic mutations: Occur in body cells → not inherited.

Genetic Terms

  • Wild-type: Most common allele/genotype.
  • Variant: Mutant allele altering phenotype.
  • Forward mutation: Wild-type → mutant.
  • Reverse mutation: Mutant → wild-type.

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