# Describe the relationship between genes, alleles and phenotype in single gene inheritance.

> Eduqas GCSE Biology — 2.4.1 Variation · Describe · 4 marks

## Mark scheme (4 marks)

1. A gene is a section/length of DNA that codes for a particular protein / characteristic.
2. Alleles are different versions of the same gene (which may have slightly different DNA base sequences).
3. A dominant allele is always expressed in the phenotype when present; a recessive allele is only expressed when two copies are present / in the absence of the dominant allele.
4. The phenotype is the physical/observable characteristic of an organism produced by the interaction between the genotype (alleles present) and the environment.

## Key terms

- [gene](https://www.gradenine.co.uk/glossary/gene)
- [allele](https://www.gradenine.co.uk/glossary/allele)
- [phenotype](https://www.gradenine.co.uk/glossary/phenotype)

## Related

- [Revision notes for Eduqas GCSE Biology](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-the-relationship-between-genes-alleles-1210173d) · Published by Druglandscape Ltd.