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NEETZoologyPrinciples of Inheritance and Variation

What is the genetic cause of Down’s Syndrome?

Options

  1. AAdditional copy of chromosome 18
  2. BAdditional copy of chromosome 21
  3. CLoss of chromosome 21
  4. DAdditional X chromosome

Correct answer

B. Additional copy of chromosome 21

Step-by-step solution

The cause of this genetic disorder is the presence of an additional copy of the chromosome number 21 (trisomy of 21) . This disorder was first described by Langdon Down (1866). The affected individual is short statured with small round head, furrowed tongue and partially open mouth (Figure 4.16). Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded

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