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GATE 2023 BT – Question 14

Genetics, Cellular and Molecular Biology · Genetics: Chromosomal variation, sex determination, genetic disorders, population genetics, epigenetics · 1 mark · Multiple choice

Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]. Assertion [a]: Chromosome mutations can change the structure of chromosomes. Reason [r]: All chromosome mutations arise due to nondisjunction of chromosomes during mitosis or meiosis.

  1. Both [a] and [r] are false
  2. [a] is true but [r] is false
  3. Both [a] and [r] are true and [r] is the correct reason for [a]
  4. Both [a] and [r] are true but [r] is not the correct reason for [a]

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Correct answer: (B) [a] is true but [r] is false

Explanation

**Assertion [a]:** Chromosome mutations change the structure of chromosomes (deletion, duplication, inversion, translocation). **True.**

**Reason [r]:** "All chromosome mutations arise due to nondisjunction." **False.** Nondisjunction is the failure of chromosomes or chromatids to separate, which changes the **number** of chromosomes (aneuploidy). Structural changes come from chromosome breakage and faulty repair or recombination, not from nondisjunction.

[a] is true and [r] is false: option **B**.