All Labs

Mitosis/Meiosis & Cell Cycle Lab

Simulate counting cells under a microscope to determine the mitotic index, estimate how long each phase lasts, and use the chi-square test to check whether observed phase counts match expected ratios.

Guided Experiment: Calculate Mitotic Index from Cell Counts

What percentage of onion root tip cells do you predict will be undergoing mitosis (not in interphase)?

Write your hypothesis in the Lab Report panel, then click Next.

Controls

Total Cells100
Noise Level10%
Interphase
Prophase
Metaphase
Anaphase
Telophase

Results

Mitotic Index=dividingtotal×100=20.0%\text{Mitotic Index} = \frac{\text{dividing}}{\text{total}} \times 100 = 20.0\%
Total Cells
100
Dividing Cells
20

Observed vs Expected Counts

Phase Proportions

Data Table

(0 rows)
#TrialTotal CellsInterphaseProphaseMetaphaseAnaphaseTelophaseMitotic Index(%)Chi-Square
0 / 500
0 / 500
0 / 500

Reference Guide

Mitotic Index

The mitotic index measures the fraction of cells actively undergoing mitosis in a tissue sample.

MI=dividing cellstotal cells×100%\text{MI} = \frac{\text{dividing cells}}{\text{total cells}} \times 100\%

A high mitotic index indicates rapid cell division, which is typical in root tips, embryonic tissue, and some tumors.

Phase Duration Estimation

The time a cell spends in a given phase is proportional to the fraction of cells observed in that phase.

tphase=nphasentotal×Tcyclet_{\text{phase}} = \frac{n_{\text{phase}}}{n_{\text{total}}} \times T_{\text{cycle}}

For onion root tip cells with a 24-hour cycle, interphase lasts about 19 hours. Anaphase, the shortest phase, takes less than 1 hour.

Chi-Square Test

The chi-square goodness-of-fit test checks whether observed phase counts differ significantly from expected proportions.

χ2=∑(Oi−Ei)2Ei\chi^2 = \sum \frac{(O_i - E_i)^2}{E_i}

With df = 4 (five phases minus one), the critical value at the 0.05 significance level is 9.488. A lower statistic means the counts are consistent with expected ratios.

Cell Cycle Timing

Interphase (G1 + S + G2) is the longest part of the cell cycle, during which the cell grows and replicates its DNA.

Prophase is the longest mitotic phase. Chromosomes condense and the spindle begins to form.

Metaphase is when chromosomes align at the cell's equator.

Anaphase is the shortest phase. Sister chromatids separate and move to opposite poles.

Telophase completes division as nuclear envelopes re-form and cytokinesis begins.