Mutations (Leaving Cert Biology): Revision Notes

Mutations

• Mutations can occur naturally or be caused by mutagens.
• Natural mutations occur when DNA does not copy itself correctly during cell division.
• Mutation rates are generally low as DNA has enzymes that can repair most mutations.
• Mutations can occur anywhere on the chromosome.
• Changes in DNA may prevent the production of important proteins, which can cause serious problems for the cell.
• Mutations in somatic cells (body cells) can lead to cancer.
• Mutations in gametes (reproductive cells) are more serious because they can be passed to offspring, affecting all their cells.

Causes of Mutations

• Many mutagens are carcinogens (cancer-causing agents).
• Examples of mutagens:
  • Radiation: UV rays, X-rays, gamma rays.
  • Chemicals: Cigarette smoke, caffeine, formaldehyde.

Types of Mutations

1. Gene mutations
2. Chromosome mutations

1. Gene mutations

• Gene mutations (also called point mutations) occur when there is a change in a single gene.
• Example: Sickle cell anaemia
  • Caused by a change in the gene for haemoglobin.
  • Results in misshapen haemoglobin proteins, forming sickle-shaped blood cells.
  • These cells can block blood vessels, carry less oxygen, and cause health problems.

2. Chromosome mutations

• Chromosome mutations occur when there is a change in the structure or number of one or more chromosomes.
• Example: Down's Syndrome
  • Occurs when the diploid number of chromosomes is 47 instead of 46.
  • This happens when a gamete (usually an egg) with 24 chromosomes combines with a normal gamete with 23 chromosomes.