📚 CBSE Grade-10 Study Guide Open in the Study Guide single page app →
Home › Science

Science — CBSE Class 10 board question

Q1. [1]
The number of chromosomes in parents and offsprings of a particular species undergoing sexual reproduction remain constant due to :
  1. (a) doubling of chromosomes after zygote formation.
  2. (b) halving of chromosomes after zygote formation.
  3. (c) doubling of chromosomes before gamete formation.
  4. (d) halving of chromosomes at the time of gamete formation.
Previously asked in CBSE board exam
2023 31/4/1 Q12
Generated by claude-sonnet-4-6 · 2026-06-15 06:43 · grounding rag
Model Answer

(d) halving of chromosomes at the time of gamete formation.

Meiosis halves the chromosome number in gametes; when two gametes fuse at fertilisation, the original chromosome number is restored in the offspring.

Explanation

The source passage (7.3.1) explicitly states that germ-cells are formed by meiosis, which results in half the number of chromosomes. Fusion of two such gametes (fertilisation) restores the full chromosome number in the zygote — keeping it constant across generations. Options (a), (b), and (c) describe incorrect stages or incorrect processes.

If a question refers to an image, map, graph or diagram that is not shown here, open the Study Guide single page app, go to Library and find the actual CBSE question paper. The original papers are also available on the CBSE website: cbse.gov.in.
Previous-year CBSE Grade 10 board exam questions, organised by subject and chapter, each with a model answer — free to read and print.