The chromosome number of a cell before and after the process of meiosis is conventionally represented as?

Analyze the question You're asked how chromosome number changes from the start of meiosis (the parent cell) to the end (the daughter cells).

Explain the concept

• n is the haploid number (one set of chromosomes).
• 2n is the diploid number (two sets, one from each parent).
• Meiosis is called reduction division because it halves the chromosome number. It happens in the reproductive organs to make gametes (sperm and egg cells in animals, spores in plants).
• Meiosis involves two divisions (Meiosis I and Meiosis II) but only one round of DNA replication.

Step-by-step solution

1. The parent cell that enters meiosis is diploid, so it is 2n. In humans, this is 46 chromosomes.
2. DNA replicates once, then the cell divides twice.
3. Meiosis I separates the homologous chromosome pairs, which reduces the number from 2n to n.
4. Meiosis II separates the sister chromatids, much like mitosis, so the number stays at n.
5. The result is 4 daughter cells, each haploid (n). In humans, this is 23 chromosomes.

So the change is 2n → n.

Checking the options

• A. 2n → 2n: this describes mitosis, not meiosis.
• B. n → n: this does not describe a reduction.
• C. n → 2n: this describes fertilization, where two gametes fuse.
• D. 2n → n: this is correct for meiosis.

Exam tip Remember: Meiosis = Minus (the number is reduced to half), and Mitosis = Same (the number stays the same). Fertilization restores 2n, so the chromosome number stays constant from generation to generation.