Question

In recent past, human chromosomes have been studied by a technique using specific, often fluorescent dyes, known as
A. Dyeing technique
B. Banding technique
C. Ultra dyeing technique
D. Karyotyping technique

Answer 1

Hint: Staining of chromosomes is an important aspect of analysing them. By using different stains, we can observe different parts of a chromosome such as the arms and the centromere. The chromosomal analysis gives us a good idea about the possible genetic disorders by pointing out the deletions, duplications, and other structural rearrangements.

Complete answer:
In the recent past, human chromosomes have been studied using the banding technique, which uses specific dyes. Chromosome banding is a technique by which the structure and number of chromosomes are studied. It is a form of cytogenetic analysis in which dividing cells are stained with specific dyes and observed under the microscope. As the name implies, this technique results in a band pattern along the length of the chromosomes.

There are different types of banding techniques:
> G-Banding
This is one of the most common banding techniques and it is done using a non-fluorescent stain – Giemsa stain.
Before staining, the chromosomes are treated with trypsin. Once the chromosomes are stained, they are observed under a bright-field microscope.’
A reproducible band pattern is observed on the chromosomes. Sequences that are rich in AT content stain dark, whereas sequences rich in GC content stain light.

> Q-Banding
In this technique, a fluorescent dye called quinacrine is used. When the chromosomes are exposed to a UV light, bright bands can be observed on a dark background.
This method can determine abnormalities in the chromosomes.

> C-Banding
This technique is also known as centromeric heterochromatin staining. The chromosomes are first treated with alkali and then stained with Giemsa stain.
The banding pattern is observed under a bright-field microscope.

> R-Banding
This is also known as reverse chromosome banding technique. The pattern produced is the reverse of that produced in G and Q banding. This is also done using the Giemsa stain.

Hence, the correct answer is option (B).

Note: Chromosome analysis through the banding technique can only be done on dividing cells. So, cells that are in the metaphase stage of mitosis are taken.
- In plants, the meristematic cells of the plants and root are taken for chromosomal analysis.
- For analysis in animals/humans, the cells are taken from an embryo.