How one allele can shape a visible trait
For many genes, a person inherits two copies—called alleles—one from each biological parent. If the copies differ, their effects may not contribute equally to the trait. In a simple dominant–recessive pattern, one dominant allele is enough to produce the version of the trait associated with it. The recessive allele is still present in the person’s DNA, but its effect is not apparent in that particular trait.
Hidden does not mean inactive or gone
A recessive allele can be passed on because either copy of a gene may be transmitted to a child. If a parent carries one dominant and one recessive allele, each child has a chance of inheriting either one. A child who receives the recessive allele may therefore carry it too, even if the trait is not visible.
If both parents pass on a recessive allele for the same gene, their child may inherit two recessive copies. In the simple pattern, with no dominant copy to mask them, the recessive-associated trait can then appear. This is why a trait may turn up in a family even when neither parent shows it.
A useful model, not a rule for every trait
Dominant and recessive describe how particular alleles relate to a particular trait; they do not mean “stronger” and “weaker,” or more common and less common. Many traits involve several genes or more complex interactions, so the simple masking model does not explain every inherited feature. But for a single-gene trait that follows this pattern, the key distinction is straightforward: the visible version does not tell the whole story of which alleles a person can pass on.
