Down Syndrome: Trisomy 21 Etiology
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Questions and Answers

What is the primary cause of full trisomy 21?

  • Maternal inheritance
  • Hereditary transmission
  • Paternal inheritance
  • Meiotic nondisjunction (correct)

    • Approximately what percentage of full trisomy 21 cases occur due to paternal nondisjunction during spermatogenesis?

  • 30%
  • 20%
  • 5% (correct)
  • 10%

    • What is the karyotype of a male individual with full trisomy 21?

  • 49,XY,+21
  • 47,XY,+21 (correct)
  • 48,XY,+21
  • 46,XY,+21

    • In translocation trisomy 21, which chromosome is most commonly attached to chromosome 21?

    <p>Chromosome 14</p> Signup and view all the answers

    What is the approximate percentage of cases where a balanced translocation is inherited from a parent in translocation trisomy 21?

    <p>50%</p> Signup and view all the answers

    What is the karyotype of an individual with a balanced Robertsonian translocation?

    <p>45,XX,t(14;21)</p> Signup and view all the answers

    What is the result of an unbalanced Robertsonian translocation?

    <p>Three copies of genetic material from chromosome 21</p> Signup and view all the answers

    What is the cause of mosaic trisomy 21?

    <p>Nondisjunction during mitosis</p> Signup and view all the answers

    What determines the phenotypic expression of mosaic trisomy 21?

    <p>The ratio of healthy to trisomic cells</p> Signup and view all the answers

    What is the karyotype of an individual with mosaic trisomy 21?

    <p>46,XX/47,XX,+21</p> Signup and view all the answers

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