Molecular Basis of Inheritance
Drag one slider and watch 2 metres of DNA fold all the way down to a 10,000× compacted chromosome. Walk the five packing levels in 3D — naked double helix → nucleosomes (beads-on-a-string) → 30 nm chromatin fibre → looped domains → the condensed metaphase chromosome — with the packing ratio climbing 1× → ~10,000× at every step.
drag the slider to climb the 5 packing levels · drag the model to rotate
5 minutes · +4 right, −1 wrong (real NEET marking) · one global leaderboard.
DNA is packaged in a hierarchy of increasingly condensed levels: (1) the naked DNA double helix, (2) nucleosomes — DNA wrapped around histone octamers, giving the 'beads on a string' appearance, (3) the 30 nm chromatin fibre, where nucleosomes coil into a solenoid, (4) looped domains attached to a protein scaffold, and (5) the fully condensed metaphase chromosome.
From the naked double helix to the fully condensed metaphase chromosome the DNA is compacted roughly 10,000-fold. This is why about 2 metres of DNA in each human cell can fit inside a nucleus only about 10 micrometres across.
The 30 nm fibre is the second major level of packaging. The 'beads on a string' (10 nm) array of nucleosomes coils up into a thicker, 30-nanometre-wide solenoid-like fibre, with about six nucleosomes per turn. The linker histone H1 helps stabilise this higher-order coiling.
Euchromatin is loosely packed, lighter-staining chromatin that is transcriptionally active. Heterochromatin is densely packed, darker-staining and transcriptionally inactive. Both are made of the same packaging machinery — the difference is how tightly the chromatin is condensed.
Each human cell contains about 2 metres of DNA that must fit inside a nucleus only ~10 µm wide. Packaging compacts the DNA roughly 10,000-fold so it physically fits, protects it from damage, and lets the cell organise, segregate and regulate which genes are switched on.
Yes. DNA packaging is part of the Class 12 chapter 'Molecular Basis of Inheritance' and is frequently tested in NEET. Common questions cover the order of the packaging levels, the role of histones and H1, the nucleosome composition, the 30 nm fibre, and the euchromatin vs heterochromatin distinction.
The correct sequence of DNA packaging from the least to the most condensed level is: