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.

* Dominant means that one allele masks the effect of the other allele in a heterozygous individual.

For example, if you have the alleles for brown eyes (B) and blue eyes (b), and brown eyes are dominant, then you will have brown eyes because the "B" allele masks the effect of the "b" allele.