Science
Dominant and recessive traits.
Definition
A dominant allele expresses its phenotype even when only one copy is present (heterozygous), while a recessive allele only shows its phenotype when two copies are present (homozygous recessive). This concept was first described by Gregor Mendel.
Examples
Real-world.
- 1 Brown eye color (B) is dominant over blue (b), so Bb individuals have brown eyes
- 2 Huntington's disease is caused by a dominant allele—only one copy is needed to develop the condition
- 3 Cystic fibrosis is recessive—a person must inherit two copies of the recessive allele (ff) to be affected
Key Fact
Dominant = expressed in Bb (heterozygous); Recessive = only expressed in bb (homozygous recessive).