Which dye is not used to stain chromosome ?

Question

Accepted Answer

The correct option is (3): Safranin

The question asks you to identify the dye that is not typically used for staining chromosomes in cytological and histological studies. The correct answer is Safranin because its primary and most widespread application lies in other areas of biological staining, rather than specifically targeting the DNA-rich structure of the chromosome. Safranin is a basic (cationic) dye, which means it has an affinity for negatively charged components, such as the phosphate backbone of DNA. However, it is overwhelmingly known for its use as a counterstain in plant histology, where it selectively stains lignified and cutinized cell walls (like xylem) bright red, making them visible against the blue background provided by a primary stain. It is also the crucial last step in the Gram staining procedure for bacteria. While a basic dye *could* potentially stain chromatin, Safranin lacks the specific, high affinity for condensed mitotic chromosomes that the other options possess, rendering it an unsuitable primary stain for clear chromosomal analysis.

The incorrect option is (1): Feulgen

Feulgen is not just a dye but a specific histochemical reaction, making this option incorrect. The Feulgen reaction is considered the most specific staining method for DNA, which is the main component of chromosomes. The technique involves mild hydrolysis of the cell nuclei with acid, which removes purine bases from the DNA, thereby creating aldehyde groups. Schiff’s reagent, which is the "Feulgen" component, then reacts with these aldehyde groups to produce a characteristic, vivid purple or reddish-purple color, precisely marking the location of the DNA—and therefore the chromosomes—in the cell. It is a fundamental technique for quantitative DNA analysis.

The incorrect option is (2): Acetocarmine

Acetocarmine is one of the oldest, simplest, and most effective stains used in cytogenetics, making this an incorrect option. It is a brilliant red-colored dye dissolved in acetic acid, and it is a popular choice for studying meiosis and mitosis, especially in rapid preparations of plant tissues, such as root tips and pollen mother cells. The acetic acid acts as both a fixative and a mordant, allowing the carmine dye to strongly bind to the chromatin, thus clearly delineating the chromosomes for microscopic observation. This technique is routinely employed for immediate examination of chromosomes in temporary mounts, often called a "squash preparation."

The incorrect option is (4): Haematoxylin

Haematoxylin is a primary stain in histology and cytology, making this an incorrect option. It is the key component of the H&E (Haematoxylin and Eosin) staining procedure, the standard technique used to examine tissue sections under the microscope. In conjunction with a mordant (typically an aluminum salt), haematoxylin acts as a basic dye, staining the negatively charged nucleic acids—DNA—in the cell nucleus (and therefore the chromosomes) a distinct blue or purple color. This strong basophilia of the chromatin allows for excellent visualization of nuclear structure and mitotic figures, making it an essential chromosome stain.