Mutations

This lesson covers mutations — changes in the DNA base sequence — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the different types of mutation, how mutations affect proteins, and whether mutations are beneficial, harmful or neutral.

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What Is a Mutation?

A mutation is a change in the base sequence of DNA. Since the base sequence determines the order of amino acids in a protein, a mutation can change the protein that is produced.

Mutations can occur:

• Spontaneously — random errors during DNA replication (e.g. during cell division)
• Due to mutagens — environmental factors that increase the rate of mutation

Common Mutagens

Mutagen	Example
Radiation	UV light, X-rays, gamma rays
Chemicals	Tar in cigarette smoke, certain dyes
Biological	Some viruses can insert DNA into host cells

Exam Tip: Mutations are random — they are not caused by an organism "needing" to change. This is a common misconception that examiners will test.

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Types of Gene Mutation