Class 12 Botany simulations · Molecular Basis of Inheritance

Semiconservative replication (Meselson–Stahl)

Grow E. coli in ¹⁵N, then switch to ¹⁴N. Spin the DNA in a CsCl gradient after each generation.

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What to notice

After one generation all DNA is hybrid (¹⁵N/¹⁴N) — exactly what semiconservative replication predicts.

Key relation

After generation n (n ≥ 1): hybrid fraction = 1/2ⁿ⁻¹ ; light fraction = 1 − 1/2ⁿ⁻¹

Try this

After two generations, what fraction of DNA is light?

What you can change

• Generations in ¹⁴N: 0 to 5

More in Molecular Basis of Inheritance

• Transcription and translation
• DNA double helix
• DNA fingerprinting with VNTRs
• The lac operon

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