Mitotic Index Calculator
Calculate the mitotic index: percentage of cells in mitosis at any given time. Observe cell division stages and calculate fraction of actively dividing cells from microscopy data.
🦠 Cell Biology📐 MI = (cells in mitosis / total cells) × 100🧬 Biology
Cells in mitosis (all stages)
Total cells observed
Cells in prophase
Cells in metaphase
Cells in anaphase
Cells in telophase
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Mitotic Index Calculator | — | MI = (cells in mitosis / total cells) × 100 | % |
Step-by-Step Examples
Example 1
Onion root tip
Count 200 cells: 15 in mitosis (prophase=8, metaphase=4, anaphase=2, telophase=1).
- MI = 15/200 × 100 = 7.5%
- Time in mitosis ≈ 7.5% × 24h = 1.8h
- Most cells are in interphase (growth)
✓ Mitotic index = 7.5%
Example 2
Cancer tissue
Biopsy: 200 cells counted, 40 in mitosis.
- MI = 40/200 × 100 = 20%
- High MI: rapid proliferation, indicates cancer activity
- Normal tissue: MI < 1%
✓ MI = 20% (highly proliferative tumor)
Example 3
Colchicine arrest
After colchicine treatment: all dividing cells arrested in metaphase.
- All mitotic figures are metaphase plates
- Count metaphase plates/total cells = fraction of cells that were in active division
- Used to determine cell cycle distribution
✓ Metaphase arrest quantifies S/G2/M fraction
Real-World Applications
Cancer Pathology
High mitotic index is a key diagnostic criterion for malignancy. Used in tumor grading.
Oncology
MI predicts tumor aggressiveness. Chemotherapy targets mitotic cells.
Cell Biology Research
Study cell cycle regulation, synchronization, and effects of cell cycle checkpoint drugs.
Plant Biology
Root tip squashes to observe plant mitosis and study cell cycle in classical genetics labs.
Common Mistakes to Avoid
⚠️
Count only unambiguous mitotic figures
Prophase chromatin condensation can resemble apoptotic cells. Count only clear mitotic figures with visible chromosomes.
⚠️
Count ≥500 cells for reliable MI
With 200 cells: 15% CV. With 500 cells: 9% CV. Low MI (1%) requires counting thousands of cells for accuracy.
⚠️
Different tissues have different baseline MI
Gut epithelium: MI ≈ 5-10%. Liver hepatocytes: MI < 0.1%. Neurons: MI ≈ 0%. Always compare to appropriate normal tissue.
Frequently Asked Questions
What does mitotic index tell us? ▾
Fraction of cells actively dividing at any moment. Related to growth fraction and cell cycle length. MI = (duration of mitosis / total cell cycle time) × growth fraction.
What are the stages of mitosis? ▾
Prophase (chromatin condenses, nuclear envelope breaks down), Metaphase (chromosomes align), Anaphase (sister chromatids separate), Telophase/Cytokinesis (two daughter cells form).
Why does prophase dominate the MI? ▾
Prophase is longer than metaphase, anaphase, telophase combined. In onion root: prophase takes 36 min of ~70 min total mitosis. Metaphase: 20 min.
How is MI used in cancer grading? ▾
Mitotic count per high-power field (HPF) is one of three criteria in the Bloom-Richardson grading system for breast cancer. > 10 mitoses/10 HPF = grade 3.
What is the thymidine labeling index? ▾
Fraction of cells synthesizing DNA (S phase) after exposure to tritiated thymidine or BrdU. Similar concept to MI but for DNA synthesis rather than visible mitosis.