# Dominant and recessive alleles

A dominant allele shows up even if you have only one copy. A recessive allele shows only if you have two copies.

Biology (school) · Part 05: Genes and inheritance · Card 5 of 11 · Last updated 2026-10-19

## Analogy

A loud voice drowning out a quiet one.

## In practice

The allele for brown eyes is dominant to blue, so one brown allele is enough for brown eyes.

## Practice

### Flashcards

- **If a person has a dominant and a recessive allele, which shows?** The dominant one.

## Questions people ask

### Does dominant mean more common?

No. Dominant describes how an allele behaves in a person with two different alleles, not how common it is. Some dominant alleles are rare. Polydactyly, having extra fingers, is caused by a dominant allele but is uncommon. Common alleles can be recessive, such as for blood group O.

### How do you write dominant and recessive alleles?

Use the same letter for both, with a capital letter for the dominant allele and a lower-case letter for the recessive one, such as T for tall and t for short. So TT and Tt are tall, and only tt is short. Always say in the question which letter you choose.

## Related concepts

- [Genotype and phenotype](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-6)
- [Punnett square](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-7)
- [Sex chromosomes](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-10)
- [Inherited disorder](https://studyvisually.com/learn/science/biology-school/biology-school-part-5/biology-school-part-5-concept-11)

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