Genetic Disorders and Mutations

  • Chromosome structure and function

    • Genes are arranged in a specific order on chromosomes.
    • Any alteration in the gene sequence or location can lead to anomalies and recurring conditions.

  • Somatic cell mutation

    • Defined as mutations occurring in body cells (not sexual/gamete cells).
    • Includes all types of body cells such as skin and hair cells.
    • Somatic mutations are not inherited, meaning they affect the individual but cannot be transmitted to the next generation.
    • Example: A person born with a missing little finger has a somatic mutation, but this does not pass to their offspring.

  • Gamete cell mutation

    • Changes occurring in gametes (sperm or ovum) can be passed to the next generation.
    • Example: A deformity in a parent’s gametes can lead to hereditary conditions in their children.

  • Dominant vs. Recessive Genes

    • Dominant genes

    • A genetic condition inherited from one parent can manifest in the offspring.

    • Example: Dominant traits such as freckles and Huntington's disease can appear in descendants, even if the other parent is healthy.

    • Recessive genes

    • Requires both parents to have the recessive gene for the condition to manifest in the offspring.

    • Example: Sickle cell anemia requires a recessive gene from both parents.

  • Disease Transmission

    • Diseases passed down through genes characterized as:
    • Dominant disorders: One affected parent can pass the condition to their child.
      • Example: Huntington's disease, where only one parent needs a faulty dominant gene.
    • Recessive disorders: Both parents must transmit the recessive gene for the condition to manifest.
      • Example: Sickle cell anemia or cystic fibrosis, where both must be carriers.

  • Genetic disorders

    • Sickle Cell Anemia: A blood disorder caused by the presence of abnormal hemoglobin, leading to sickle-shaped red blood cells.
    • Down Syndrome (Trisomy 21): An inherited condition caused by the presence of an extra chromosome 21, leading to developmental and physical abnormalities.
    • Cystic Fibrosis: A genetic disorder that affects the respiratory and digestive systems, leading to the production of thick, sticky mucus.
    • Hemophilia: A sex-linked disorder affecting blood clotting, typically passed from mothers to sons through the X chromosome.
    • Huntington's Disease: A dominant genetic disorder that results in progressive neurological decline.
    • Muscular Dystrophy: A group of genetic disorders characterized by progressive weakness and degeneration of the skeletal muscles.
    • Phenylketonuria (PKU): A metabolic disorder caused by the absence of the enzyme needed to break down phenylalanine, leading to mental retardation if untreated.

  • Key differences between Genetic and Congenital Disorders

    • Genetic disorders: Conditions caused by defective genes, which can be inherited.
    • Congenital disorders: Disorders present at birth that may not always be genetic, such as those caused by environmental factors.

  • Clinical note: Genetic disorders can often be managed or ameliorated through medical interventions, and early detection is crucial.