# Huntington's disease is a genetic disorder caused by a dominant gene mutation. A person who has one copy of the dominant allele for Huntington's disease will develop the condition. Explain how a gene mutation can lead to a genetic disorder such as Huntington's disease, and why having just one copy of the dominant allele is enough to cause the condition.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.5 Gene mutations and genetic disorders · Explain · 5 marks

> Huntington's disease affects the nervous system and causes progressive loss of muscle control. It is caused by a dominant allele that can be inherited from one parent.

## Mark scheme (5 marks)

1. A gene mutation is a change in the DNA/base sequence of a gene
2. The mutation changes the sequence of amino acids in the protein produced / leads to a different protein being made
3. The altered protein cannot carry out its normal function / the protein does not function correctly
4. The dominant allele masks the effect of the recessive allele / only one copy of the dominant allele is needed to express the condition
5. Therefore even if only one parent passes on the dominant allele, the offspring will be affected / a heterozygous person will still develop Huntington's disease

## Key terms

- [gene mutation](https://www.gradenine.co.uk/glossary/gene-mutation)
- [dominant allele](https://www.gradenine.co.uk/glossary/dominant-allele)
- [genetic disorder](https://www.gradenine.co.uk/glossary/genetic-disorder)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/huntington-s-disease-is-a-genetic-disorder-dc05f899) · Published by Druglandscape Ltd.