Q.Name a stain commonly used to colour chromosomes.

Chromosomes need to take up a dye strongly to stand out clearly under a microscope, and one particular stain is the standard choice used for exactly this purpose in cytology.

• Acetocarmine (aceto-carmine) is a red/carmine dye dissolved in acetic acid that binds strongly to chromosomal DNA, staining condensed chromosomes a deep red-pink while leaving the surrounding cytoplasm comparatively unstained. …

To study chromosome number, shape and structure, a tissue sample (commonly a root tip, where cells are actively dividing) is squashed and stained so that condensed chromosomes become clearly visible against the rest of the cell. This works because chromosomes are only sharply distinct once condensation is complete — a process that finishes by metaphase, when the DNA has coiled into compact, individually visible structures.

The stain conventionally used for this is acetocarmine:

• It is prepared by dissolving carmine dye in acetic acid.
• It binds strongly to chromosomal DNA/chromatin, staining condensed chromosomes a deep red to pink colour.
• The surrounding cytoplasm takes up far less of the stain, so the coloured chromosomes stand out sharply against a much lighter background. …

Method: Recall the standard cytological stain used for chromosome studies

1. Chromosome studies (e.g. root-tip squash preparations) require a dye that binds DNA/chromatin strongly so condensed chromosomes stand out under the microscope.
2. The standard stain taught for this purpose is acetocarmine (aceto-carmine) — a red/carmine dye dissolved in acetic acid that stains chromosomal DNA deep red/pink while leaving the cytoplasm relatively unstained. …