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.
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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.