Science (086) — CBSE Class 10 board question

Reason: In sexual reproduction, the gametes (sperm and egg) are formed by a special cell division called meiosis, which reduces the number of chromosomes to half (haploid) in each gamete. During fertilisation, the male gamete fuses with the female gamete to form a zygote. This fusion restores the original (diploid) number of chromosomes. Thus, the zygote — and the organism that develops from it — has the same number of chromosomes as the parents.

Example: If a parent cell has 46 chromosomes, each gamete has 23. After fertilisation, the zygote again has 46 chromosomes.

Source: Chapter 7, Section 7.3.1 – Why the Sexual Mode of Reproduction?

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• The key concept is meiosis → haploid gametes → fertilisation → diploid zygote.
• Examiners expect you to mention: (1) meiosis halves the chromosome number, (2) fertilisation restores it.
• Use the terms haploid, diploid, gametes, zygote, and meiosis — these earn marks.
• Don't just say "chromosomes are maintained" — explain the mechanism (meiosis + fertilisation).