31. Eukaryotic genomes are organized into chromosomes and can be visualized at mitosis by staining with specific dyes. Heat denaturation followed by staining with Giemsa produced alternate dark and light bands. The dark bands obtained by this process are mainly
(1) AT -rich and gene rich regions.
(2) AT -rich and gene desert regions.
(3) GC-rich and gene rich regions.
(4) GC-rich and gene desert regions.
The correct answer is (2) AT-rich and gene desert regions. In G-banding (heat denaturation followed by Giemsa staining), dark bands (G-bands) correspond to heterochromatic regions that are AT-rich, late-replicating, and gene-poor (“gene deserts”), while light bands (R-bands) are euchromatic, GC-rich, early-replicating, and gene-rich.
Option Analysis
-
(1) AT-rich and gene rich regions: Incorrect. Although dark bands are AT-rich, they are gene-poor, not gene-rich; gene-rich regions align with light, GC-rich bands.
-
(2) AT-rich and gene desert regions: Correct. Giemsa-dark bands are locally AT-rich (GC-poor relative to surroundings), heterochromatic, and contain fewer genes, forming gene deserts due to condensed chromatin and late replication.
-
(3) GC-rich and gene rich regions: Incorrect. GC-rich regions produce light bands, which are transcriptionally active and gene-dense, not dark bands.
-
(4) GC-rich and gene desert regions: Incorrect. GC-rich areas are gene-rich, not deserts; gene deserts are tied to AT-rich dark bands.
Giemsa staining dark bands AT-rich regions reveal key features of eukaryotic chromosome organization during mitosis. Heat denaturation followed by Giemsa dye creates alternate dark and light bands, where dark bands (G-bands) highlight condensed heterochromatin. These AT-rich zones, visualized in karyotyping, aid genetic analysis and exam questions on chromosome structure.
Dark Giemsa bands are mainly AT-rich gene desert regions, differing from light GC-rich gene-rich bands. This pattern arises from trypsin or heat treatment exposing AT-preferring dye binding in gene-poor areas. For CSIR NET aspirants, understanding this distinguishes replication timing and chromatin density.
