MUTATIONS

Mutations Overview

  • Mutations refer to changes in genetic material which can lead to variations in traits and may influence evolution.

Definition of a Gene

  • A gene is a section of DNA, acting as a blueprint for the body's functions and characteristics.

What is a Genetic Mutation?

  • A genetic mutation is a heritable change in the DNA sequence, which can result in a structural change of DNA.

Causes of Mutations

  • Mistakes in DNA Replication: Errors during the DNA copying process can lead to mutations.

  • Exposure to Mutagens: Mutagens include radioactive substances, x-rays, ultraviolet radiation, and certain chemicals.

  • Viral Infections: Some mutations can be triggered by infections from viruses.

Brief History of Mutations

  • Hugo de Vries: Coined the term mutation in the 1900s.

  • Seth Wright: Recorded the first case of mutation in 1791, observing a male lamb with unusually short legs.

Classifications of Mutations

Based on Survival of the Individual

  • Lethal Mutation: 100% death rate.

  • Sub Lethal: 90% death rate.

  • Sub Vital: Less than 90% death rate.

  • Vital Mutation: No effect on survival.

  • Super Vital: Increased survival rate.

Based on Tissue Origin

  • Spontaneous Mutation: Occurs naturally.

  • Induced Mutation: Caused by chemical or physical factors.

  • Somatic Mutation: Occurs in somatic cells.

  • Germinal Mutation: Occurs in gametes.

Based on Traits and Mutation Direction

  • Visible Mutation: Observable physical alteration.

  • Chemical Mutation: Affects biochemical production.

  • Forward Mutation: Changes normal/wild allele to mutant allele.

  • Reverse Mutation: Converts mutant allele back to normal/wild allele.

Types of Mutations

  • Point Mutation: A change in a single base pair, akin to a spelling mistake in DNA.

  • Chromosome Mutation: Involves larger structural changes in chromosomes.

  • Genome Mutation: Changes affecting the entire genetic material.

Point Mutations

  • Addition (Insertion) Mutation: A base pair is added.

  • Deletion Mutation: A base pair is removed.

  • Example: A G (guanine) might be swapped for a C (cytosine).

Types of Point Mutations

  1. Silent Mutation: No change in amino acid.

  2. Missense Mutation: Alters one amino acid.

  3. Nonsense Mutation: Creates a stop codon, truncating the protein.

Related Diseases Due to Mutations

  • Sickle Cell Disease: Caused by a point mutation affecting hemoglobin.

  • Cystic Fibrosis

  • Tay-Sachs Disease

  • Duchenne Muscular Dystrophy (DMD)

  • Huntington’s Disease

Chromosomal Mutations

  • Involves changes in the structure of chromosomes such as deletions, duplications, inversions, and translocations which can lead to genetic disorders or cancer.

Genomic Mutations

  • Changes in the number of chromosomes.

  • Aneuploidy: Having an extra or missing chromosome (e.g., Down syndrome).

  • Polyploidy: Having extra sets of chromosomes, common in plants.

Evolution and Mutations

  • Some mutations can provide a survival advantage, resulting in new traits that may lead to species evolution.

Real-Life Example: Sickle Cell Anemia

  • Caused by a point mutation where A (adenine) is replaced by T (thymine), affecting hemoglobin production.