Module 6 - Genetic Change: 6.1 Mutation

6.1 Mutation

  • Mutation introduces new alleles into a population.

Objectives

  • 6.1.1: Explain how a range of mutagens operate, including but not limited to:

    • Electromagnetic radiation sources

    • Chemicals

    • Naturally occurring mutagens

    • Explain: Relate cause and effect; make the relationships between things evident; provide why and/or how

What is a Mutagen?

  • Any substance, process, or agent that can cause a mutation to occur in the sequence or structure of DNA.

  • Mutagens can be artificial or naturally occurring.

  • Mutagens can be beneficial in the evolution of a species by generating potentially beneficial and successful variations.

  • Mutations can be harmful, preventing the correct synthesis of a protein.

  • Mutations can be harmless if they occur in the non-coding section of a gene

  • Mutagens can be classified as chemical, physical, or biological.

Physical Mutagens

  • Radiation: The movement of energy through space and materials.

  • Only high-frequency radiation such as UV, X-rays, and gamma radiation can cause damage to DNA.

Physical Mutagens: X-rays and Gamma Rays

  • Direct mutations: High-energy radiation can break the sugar-phosphate backbone of a strand of DNA, sometimes allowing a whole section of a chromosome to be distorted or displaced.

  • Indirect mutations: Radiation causes other molecules to lose an electron, and these molecules (reactive intermediates) can then interact with DNA to cause mutation.

Chemical Mutagens

  • Intercalating agents: Chemicals that insert themselves into the bonds between base pairs and alter the shape of the DNA, leading to subsequent errors in replication.

  • Base analogues: Chemicals that are structurally similar enough to that of the nitrogenous bases in DNA that they are incorporated into the DNA sequence during replication instead of the usual bases, meaning that the DNA no longer functions.

  • DNA Reactive chemicals (e.g., Reactive Oxygen Species): Chemicals that react directly with DNA, which cause breakages in the DNA strand

Biological Mutagens

  • Living molecules that can cause mutations and cancers by interfering with the functions of oncogenes (genes that have the potential to cause cancer) and tumor-suppressor genes.

  • Viruses:

    • Retroviruses insert their genetic information into the chromosomes of the host cell and can account for diseases such as leukemia.

    • Oncogenic viruses can directly introduce oncogenes, or they can cause prolonged chronic inflammation that can indirectly cause cancer.

  • Transposable elements: Short segments of DNA that move around the genome. They cause errors in replication and can insert themselves into the middle of gene sequences.

Naturally Occurring Mutagens

  • Can be biological or non-biological.

  • Non-biological: Metals such as mercury and cadmium.

  • Biological: Viruses, bacteria, fungi, and their products.

  • Natural sources of radiation: Cosmic radiation, electromagnetic radiation from the sun, radiation from radionuclides of uranium, thorium, and potassium in rocks and soils.

  • Natural sources of chemicals: Chemicals produced by incomplete burning (bushfires), benzene found in crude oil and coal.

Carcinogens

  • Mutagens that cause the formation of cancerous cells.

  • They cause the affected cells to divide uncontrollably because the mutagen damages the DNA.

  • Examples include: tobacco, radon, asbestos, UV rays, Helicobacter pylori.