Question

The stain used by Feulgen to stain DNA is
A. Janus green
B. Basic fuchsin
C. Crystal Violet
D. Methylene blue

Answer 1

DNA is genetic material found in almost all cells, either prokaryotic or eukaryotic cells. It transfers hereditary or genetic information from one generation to another generation. In eukaryotes, it is found in the form of chromosomes within the nucleus.

Complete answer:
Feulgen staining procedure or method is used for the staining of DNA present within the nucleus. This technique selectively stains DNA in controlled conditions. The material to be stained is first treated with 1N HCl at 60 0 C. Then, the material is treated with Schiff reagent, which contains basic fuchsin.

The treatment of acid causes hydrolysis, which removes purine bases DNA. It is called depurination and it produces small fragments of DNA. When it is treated with Schiff’s reagent, it produces purple colour with DNA only. RNA is not depurinated hence it gives no colour. Janus green is a basic dye and vital stain. It is used in Histology for staining of mitochondria.

Basic fuchsin is used for the staining of nucleus and in the staining of acid fast bacteria like Mycobacterium tuberculosis in Ziehl - Neelsen staining. Crystal violet is also called methyl violet. It is used for staining in histology and in bacterial Gram staining. Methylene blue is used as counterstain staining of bacteria.

Hence, the correct answer is option (B).

Note: Staining is a method, which is used in microbiology. It generates contrast in microorganisms. It helps to visualize microorganisms like bacteria more clearly when seen through a compound microscope.