An "Anti back staining agent" is a chemical used to prevent back staining when cells stain their chromosomes. This substance is often used when viewing a cell's chromosomes under a microscope.
When a cell's chromosomes are viewed under a microscope, the cells are stained to make the chromosomes easier to see. However, sometimes other parts of the cell, such as the nuclear envelope or organelles, are also stained, which is known as "backstaining." This can blur the image of the cell's chromosomes and can affect the results of the analysis of the cell. The use of counter-staining agents can effectively prevent this from happening, so that the image of observing cell chromosomes is clearer.