Cell Cycle and Mitosis Lab

A teaching model, not a real cell line. Phase lengths are typical for cultured human cells (G1 about 10 h, S 8 h, G2 4 h, M about 1 h) with random variation, and time is sped up (simulated hours per second shown). Cells are drawn with 2n = 4. The dish holds about 140 cells in one layer. Growth factor below about 15% sends cells to G0. Damaged cells with normal p53 pause in G1 or G2 to repair, and some undergo apoptosis; with mutant p53 the G1 stop and apoptosis fail and only a brief G2 pause remains, so damage is passed on. Spindle poisons hold cells at the M checkpoint, and long arrests end in cell death. Overexpressed G1 cyclin pushes cells past the G1 checkpoint even without growth factor or space (simplified).

A drawn, stained onion root tip (chromosomes dark purple). Click or tap a cell to select it, or use Previous and Next. Real slides are messier: cells can be cut at angles and stages blend into each other. Stage proportions are typical of a root tip meristem.

Problems are randomly generated. Cells with large chromosome numbers are drawn with a few representative chromosomes; the problem text gives the real 2n. The worked solution appears line by line, with units cancelling (struck through in red) where there is arithmetic.