One Genome, Many Switches

You'll learnhow gene expression is switched on and off without changing the DNA sequence.

A liver cell and a skin cell carry the same DNA, base for base, and behave nothing alike. Watch a repressor let go of an operator and a gene switch on without a single letter changing, then watch the two operons students always invert run opposite ways for a reason you can read off the job each one does. Ten short steps; press Next for each one.

10 STEPS · 6 QUICK CHECKS · SAME GENOME IN EVERY CELL · REGULATION IS NOT MUTATION · lac INDUCIBLE (OFF → ON) · trp REPRESSIBLE (ON → OFF) · v5

one genome · what changes is expression, never the sequence

Before you start

What you're looking at

Two cell panels — a liver cell and a skin cell — each showing the same five gene loci as boxes, some lit and some dark.

The question

If every cell holds the same genes, what makes a liver cell differ from a skin cell?

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