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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation2 Marks
Question
What happens when chromosomes fail to segregate during cell division cycle? Explain your answer with an example.
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Answer

  1. The failure of chromosomes to segregate during cell division cycle i.e., non-disjunction leads to aneuploidy, i.e., loss or gain of chromosome(s).
  2. Down's syndrome results due to trisomy of 21st chromosomes, i.e., due to non-disjunction of 21st chromosomes during gamete (ova) formation
  3. When such an ovum with two copies of 21st chromosome is fertilised by a normal sperm the zygote comes to possess three copies of 21st chromosome trisomy).

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