In Q-banding experiments, the light fluorescent band indicates that the chromosomal region is rich in base pairs: (JRF Plant Science 2021)

• Q-banding is a staining technique used in cytogenetics to visualize chromosomes. Here's how it works and why the answer is G and C:
-The Dye: Q-banding uses a fluorescent dye called quinacrine.
-Binding: Quinacrine binds preferentially to AT-rich regions of DNA. However, the dye fluoresces more strongly when it's bound to GC-rich regions.
-The Result: Areas of chromosomes that are rich in guanine (G) and cytosine (C) will show up as bright fluorescent bands under a UV microscope.

🔑Key Points:
-A complete set of chromosomes in an individual is referred to as a karyotype.
-Chromosomes are visible under a microscope during the metaphase stage of cell division.
-During this phase of the cell division, each chromosome is split into its two sister chromatids that are joined at the centromere.
-These chromosomes can be arranged diagrammatically based on their total length, arm ratio, position of the secondary constrictions, etc.
-A diagrammatic representation of the karyotype is called an idiogram. It is also called a karyogram.
-In a karyogram, the homologous chromosomes are arranged in decreasing order of their size.
-The chromosomal preparation for karyotyping can be treated with specific dyes to locate the specific regions of a chromosome.
-This method is called the chromosome banding technique. It helps to detect chromosomal abnormalities.

📌 Other Options Explanations:
-Option A and B: While quinacrine does bind to adenine (A) and thymine (T), the fluorescence is not as strong as in GC-rich regions.
-Option C: This is partially correct in that quinacrine binds to A and T, but it misses the crucial point about the stronger fluorescence with G and C.