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Q127 (IAS/2000) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Genetics and evolution Answer Verified

Assertion (A) : In human beings, the females play a major role in determining the sex of the offspring. Reason (R) : Women have two- ‘X’ chromosomes.

Result
Your answer: —  ·  Correct: D
Explanation

The Assertion is false while the Reason is true. Females are genetically XX (they have two X chromosomes), so every egg carries an X chromosome — that is correct (Reason true) [1]. However, the sex of the offspring is determined by which sex chromosome the sperm contributes at fertilisation: since fathers produce sperm carrying either an X or a Y, a child’s sex depends on the paternal contribution. All children inherit an X from their mother, so females do not ‘‘play a major role’’ in determining sex; fathers do [2]. Therefore A is false and R is true, corresponding to option 4.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > 8.2.4 Sex Determination > p. 132
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > What you have learnt > p. 133
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