An allele that produces a trait in the heterozygous condition is called a dominant allele.

Here's why:

* Heterozygous: Means having two different alleles for a particular gene. For example, Aa.

* Dominant: Means that the allele's trait will be expressed even if only one copy is present.

Example:

* Let's say the gene for eye color has two alleles: "B" for brown eyes and "b" for blue eyes.

* A person with the genotype "Bb" (heterozygous) will have brown eyes because the "B" allele is dominant over the "b" allele.

In contrast, a recessive allele only expresses its trait when two copies are present (homozygous recessive). So, a person with the genotype "bb" would have blue eyes.