M4

• Gene Replacement Therapy

  An experimental technique that uses genes to treat or prevent disease to site specific locations
• Gene Editing

  DNA is inserted, deleted, modified, or replaced in the genome of a living organism targeting the insertions to site specific locations
• Inherited or genetic disorders are disorders that can be passed from one generation to the next
• Genetic disorders result from some disorder in the gene or chromosome structure
• Genetic disorders may occur

  At the moment an ovum and a sperm fuse or even earlier, in the meiotic division phase of the gametes
• 50% of 1st trimester spontaneous miscarriages are due to genetic disorders
• Genetics


  The study of the way such disorders occur
• Genes


  The basic units of heredity that determine both physical and cognitive characteristics of people
• Alleles

  The two like genes on autosomes
• Phenotype

  A person's outward appearance or the expression of genes
• Genotype

  A person's actual gene composition
• Cytogenetics

  The study of chromosomes by light microscopy and the method by which chromosomal aberrations are identified
• Genome

  The complete set of genes present (about 50,000 to 100,000)
• Chromosomes


  Storage units of genes
• DNA

  A nucleic acid that contains the genetic instructions specifying biological development
• Gregor Mendel described the principle of genetic inheritance
• When a dominant gene is paired with a nondominant (recessive) gene

  The dominant gene is always expressed in preference to the recessive gene
• Homozygous


  Having two healthy genes
• Heterozygous


  Having two unhealthy genes
• Patterns of inheritance in rare disorders

  • Autosomal recessive
  • Autosomal dominant
  • X-linked recessive
  • X-linked dominant
• Autosomal recessive

  Disease does not occur unless 2 genes for the disease are present (homozygous recessive pattern)
• Examples of autosomal recessive disorders

  • CF
  • Albinism
  • Adrenogenital syndrome
  • Tay-Sach's
  • Galactosemia
  • PKU
  • Rh-incompatibility
• Autosomal dominant

  A person has 2 unhealthy genes (homozygous dominant) or is heterozygous, with the gene causing the disease stronger than the corresponding healthy recessive gene
• 1. linked dominant inheritance


  Genes are located on and transmitted only by the female sex chromosome (X chromosome)
• 1. linked recessive inheritance

  Usually, only males will have the disorder
• Examples of X-linked recessive disorders

  • Hemophilia A
  • Christmas disease
  • Color blindness
  • Duchenne muscular dystrophy
  • Fragile X syndrome
• Multifactorial (Polygenic) inheritance

  From multiple gene combinations plus environmental factors
• Examples of multifactorial inheritance disorders

  • Heart disease
  • Diabetes Mellitus
  • Cleft palate
  • Neural Tube Defects
  • Pyloric stenosis
• Chromosomal abnormalities (cytogenic disorders)


  Abnormalities due to fault in the number/structure of chromosomes which results in missing or distorted genes
• Karyotype


  The resulting arrangement when chromosomes are photographed and displayed
• Fluorescent in situ hybridization (FISH)


  A process to identify the number of chromosomes and specific parts of chromosomes
• Nondisjunction abnormalities

  The division is uneven resulting in one sperm/ovum having 24 chromosomes and the other 22
• If a sperm/ovum with an uneven chromosome count fuses with a normal sperm/ovum, the zygote will have 47 or 45 chromosomes
• Examples of conditions related to nondisjunction

  • Down syndrome
  • Turner syndrome
  • Klinefelter syndrome
• Deletion abnormalities


  A chromosome disorder in which part of the chromosome breaks during cell division
• Translocation abnormalities

  A child gains an additional chromosome through another route
• Mosaicism


  When the nondisjunction disorder occurs after fertilization of the ovum
• Isochromosomes


  A chromosome accidentally divides not by a vertical separation but by a horizontal one
• Purposes of genetic counselling include reproduction and disorders
• Genetic counselling

  Provides concrete, accurate information about the process of inheritance and inherited disorders