---
title: "Stochastic Gene Expression: Bursting, Noise and Cell-to-Cell Variation"
description: "Transcription happens in bursts, so genetically identical cells in one flask hold different amounts of the same protein. This stop separates intrinsic from extrinsic noise and works out what each does"
canonical: https://lightmysky.com/learn/science/stochastic-gene-expression-bursting-noise-and-cell-to-cell-variation-mt_YD6DOmrvng
source: https://lightmysky.com/learn/science/stochastic-gene-expression-bursting-noise-and-cell-to-cell-variation-mt_YD6DOmrvng.md
retrieved: 2026-09-12
---

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# Stochastic Gene Expression: Bursting, Noise and Cell-to-Cell Variation

Transcription happens in bursts, so genetically identical cells in one flask hold different amounts of the same protein. This stop separates intrinsic from extrinsic noise and works out what each does to the distribution across a population.

Subject: Science · Area: Genetics & Evolution · Ages 22 to 23
Page: https://lightmysky.com/learn/science/stochastic-gene-expression-bursting-noise-and-cell-to-cell-variation-mt_YD6DOmrvng

## Ready when they can

- Distinguish intrinsic from extrinsic noise using the two-reporter experiment that separates them
- Relate burst size and burst frequency to the mean and variance of protein number per cell
- Argue when variation is a nuisance to be averaged away and when a cell uses it to pick a fate

## Lesson: Why identical cells disagree

Transcription happens in bursts. Genes flip between on and off states, so messenger RNA appears in bursts rather than as a steady drip, and each message yields its own small burst of protein. Because only a few copies of each regulator float around a cell, chance events matter. Genetically identical cells in one flask therefore hold different amounts of the same protein.

**Example.** Suppose you build a cell with two identical gene copies, one glowing red and one glowing green. If both colours rise and fall together, the whole cell is driving them: that shared swing is extrinsic noise from size, cycle stage, or surroundings. If red and green disagree inside one cell, each copy fires on its own: that private gap is intrinsic noise from small molecule numbers. Matching shifts mean shared causes, colour gaps mean private ones.

Two knobs shape the spread. Burst size is the protein made per on spell: more protein per spell raises the size. Burst frequency is how often the gene switches on: switching on more often raises the frequency. Both knobs lift the mean level, but they shape the variance differently, so reading mean and spread together reveals which knob moved.

**Tip.** To judge variation, ask what the cell wants. When a population hedges its bets, a few hardy cells survive stress and later rebuild the group, so noise is a tool. When every cell must read the same signal cleanly, noise is a nuisance to average away. Sister cells can even drift apart on purpose as feedback locks small random gaps into different fates.

**Recap.** Genes fire in bursts, two knobs tune the spread, and cells either fight the noise or put it to work.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Discrete Models Beyond the Binomial](https://lightmysky.com/learn/mathematics/discrete-models-beyond-the-binomial-mt_9zc5xYjDg_)

## Opens up

- [Single-Cell RNA Sequencing: From Droplets to a Count Matrix](https://lightmysky.com/learn/science/single-cell-rna-sequencing-from-droplets-to-a-count-matrix-mt_QCoqY7w_De)