Chromosome numbers in mitosis and meiosis: Class 11 practice
Mitosis keeps the chromosome number (2n → 2n). Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Cell division phases
The idea behind chromosome numbers in mitosis and meiosis
Mitosis keeps the chromosome number (2n → 2n). Meiosis halves it (2n → n) to form gametes; fertilisation restores 2n. DNA content doubles in S phase before division.
Step-by-step method
- Note whether the cell is diploid (2n) or haploid (n).
- Mitosis: daughter = parent. Meiosis I halves; meiosis II keeps.
- Gametes are n; zygote is 2n.
Worked example 1 (Basic)
A an onion root cell has 2n = 14. How many chromosomes are in each daughter cell after mitosis?
- Mitosis keeps the number
- Answer: 14
Worked example 2 (Standard)
An organism has 2n = 16. How many chromosomes are in a gamete, and in a zygote?
- Gamete n = 8
- Zygote 2n = 16
- Answer: 8 and 16
Worked example 3 (Challenge)
A diploid cell (2n = 78) has 3 pg DNA in G1. Give the DNA content after S phase, after meiosis I and in each gamete.
- S: 6 pg
- After meiosis I: 3 pg
- Gamete: 1.5 pg
- Answer: 6, 3 and 1.5 pg
Common mistakes and misconceptions
- Halving in mitosis
- Saying meiosis II halves again
Practice questions
- (Basic) A an onion root cell has 2n = 46. How many chromosomes are in each daughter cell after mitosis?
- (Basic) A a plant cell has 2n = 14. How many chromosomes are in each daughter cell after mitosis?
- (Standard) An organism has 2n = 48. How many chromosomes are in a gamete, and in a zygote?
- (Standard) An organism has 2n = 46. How many chromosomes are in a gamete, and in a zygote?
- (Challenge) A diploid cell (2n = 24) has 7 pg DNA in G1. Give the DNA content after S phase, after meiosis I and in each gamete.
- (Challenge) A diploid cell (2n = 16) has 6 pg DNA in G1. Give the DNA content after S phase, after meiosis I and in each gamete.
Answer key with full working
- Q1: Mitosis keeps the number → Answer: 46
- Q2: Mitosis keeps the number → Answer: 14
- Q3: Gamete n = 24 → Zygote 2n = 48 → Answer: 24 and 48
- Q4: Gamete n = 23 → Zygote 2n = 46 → Answer: 23 and 46
- Q5: S: 14 pg → After meiosis I: 7 pg → Gamete: 3.5 pg → Answer: 14, 7 and 3.5 pg
- Q6: S: 12 pg → After meiosis I: 6 pg → Gamete: 3 pg → Answer: 12, 6 and 3 pg
Syllabus note
This skill is listed under "Cell Cycle and Cell Division" for Class 11 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is chromosome numbers in mitosis and meiosis in?
"Cell Cycle and Cell Division", Class 11 Biology (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.