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NEET 2013
Exam
NEET
Year
2013
Subject
Zoology
Chapter
Principles of Inheritance and Variation

NEET 2013 · Zoology · Principles of Inheritance and Variation

Down's syndrome in humans is due to:

Down's syndrome in humans is due to:

Options

  1. Athree ' X\mathrm{X} ' chromosomes
  2. Bthree copies of chromosome 21
  3. Cmonosomy
  4. Dtwo ' Y\mathrm{Y} ' chromosomes.

Correct answer

B. three copies of chromosome 21

Step-by-step solution

Down's syndrome a genetic disorder is due to the presence of an extra chromosome 21 also known as trisomy of chromosome 21 . Related Theory Down's syndrome is caused due to abnormal cell division. During mitotic and meiotic cell division the chromosome pair separate so that each cell gets the copy of each chromosome. In Down syndrome, the chromosomes are not able to separate, giving rise to cells with an unequal number of chromosomes (nondisjunction).
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