Biology for IGCSE & O level - Inheritance (Section 11 - No. 18)
What does a recessive allele require to express its phenotype?
The presence of a dominant allele.
Two copies of the same allele.
An environmental trigger.
A mutation in a related gene.
Forklaring
A recessive allele's phenotype is expressed only when two copies are present (homozygous recessive).