3.15—Core Practical 6 - root tip squash mitosis

Root-tip meristems contain actively dividing cells, so a stained squash can show the stages of mitosis under a light microscope. Acid softens the tissue, stain makes chromosomes visible, and gentle squashing spreads cells into a thin layer.

Cut a root tip, treat and rinse it, stain the tissue, squash it carefully on a slide and observe with suitable magnification. Identify condensed chromosomes and classify cells by the visible stage rather than by where you expect them to be.

A metaphase cell has chromosomes aligned at the equator; an anaphase cell has sister chromatids moving apart. Counting every stage with visible chromosomes allows a mitotic index to be calculated.

The preparation is a snapshot of a fixed sample: it cannot show a living cell progressing through time. Do not count an unclear nucleus as a stage or damage the specimen by pressing too hard.