GENETIC DEFECTS

• Genetic defects


  Defects that result from changes to genes or chromosomes
• Types of genetic defects

  • Autosomal disorders
  • Sex-linked disorders
  • Multifactorial disorders
• Some genetic defects arise spontaneously, whereas others may be caused by environmental teratogens
• Teratogens


  Environmental agents (such as infectious toxins, maternal diseases, drugs, chemicals, and physical agents) that can cause structural or functional defects in a developing fetus
• Mutation


  A permanent change in genetic material
• Mutations can result from exposure to radiation, certain chemicals, or viruses, and can also happen spontaneously
• Cells


  • Have built-in defenses against genetic damage
  • Can identify and fix mutations to keep things working normally
• If a mutation isn't identified or repaired, it may produce a new trait that can be transmitted to offspring</b>
• Autosomal disorders


  Genetic disorders caused by an error at a single gene site on the DNA strand
• Autosomal dominant


  Transmission of an abnormal gene that's dominant
• Autosomal recessive


  Transmission of a recessive gene that's abnormal
• Sex-linked disorders


  Genetic disorders caused by genes located on the sex chromosomes
• 1. linked recessive


  Most sex-linked disorders are controlled by genes on the X chromosome, usually as recessive traits
• 1. linked dominant


  Evidence of the inherited trait usually exists in the family history
• Multifactorial disorders


  Result from a number of genes and environmental influences acting together
• Most multifactorial disorders don't appear until later in life, and environmental factors likely influence their development
• Chromosome defects


  Changes in the structure or number of chromosomes, which can lead to congenital anomalies or birth defects
• Chromosomal disjunction and nondisjunction

  1. Critical processes during cell division that determine the correct distribution of chromosomes

  2. Disruption of these processes, particularly nondisjunction, can lead to chromosomal abnormalities and genetic disorders
• Trisomy


  An example is Down syndrome, where there are three copies of chromosome 21 instead of the usual two
• Monosomy


  An example is Turner syndrome, where females have only one X chromosome instead of the typical two
• Translocation


  The relocation of a segment of a chromosome to a nonhomologous chromosome, which can lead to serious genetic defects
• The incidence of nondisjunction increases with parental age