Dominant and recessive alleles are two forms of a gene that determine how a trait appears in an organism.
- A dominant allele is the one that shows its effect even if only one copy is present. It can mask the effect of a recessive allele.
- A recessive allele is the one that is hidden or masked when a dominant allele is present. It shows its effect only when both copies are recessive.
Example:
In pea plants:
- The allele for tallness (T) is dominant.
- The allele for shortness (t) is recessive.
So:
- TT → Tall (two dominant alleles)
- Tt → Tall (dominant allele masks recessive one)
- tt → Short (no dominant allele present)
In short:
- Dominant allele = expresses the trait even with one copy.
- Recessive allele = expresses the trait only when both alleles are recessive.