Genetic Variants and Mutations

This lesson covers mutations, genetic variants (alleles), and the causes of variation. This is essential content for Edexcel GCSE Biology (1BI0) Topic 3: Genetics.

---

What Is a Mutation?

A mutation is a random, spontaneous change in the base sequence of DNA. Mutations can occur during DNA replication (when DNA is copied before cell division) or can be caused by external factors.

How Mutations Occur

• During DNA replication, the wrong base may be inserted, a base may be deleted, or extra bases may be added.
• These changes alter the sequence of bases in the gene.
• Mutations are random — they are not directed or intentional.
• Mutations are rare but occur naturally at a low frequency.

Mutagens

Certain environmental factors can increase the rate of mutation. These are called mutagens:

Mutagen	Example
Ionising radiation	UV light, X-rays, gamma rays
Chemical mutagens	Chemicals in cigarette smoke, certain industrial chemicals
Biological agents	Some viruses can insert their DNA into the host genome