The gene that is fully expressed when two different alleles are present is called a dominant allele.

Here's why:

* Alleles: Different versions of the same gene.

* Dominant: An allele that masks the expression of the other allele.

* Recessive: An allele that is only expressed if two copies of it are present.

Example:

* Brown eyes (B) are dominant over blue eyes (b).

* Someone with the genotype Bb (one brown eye allele and one blue eye allele) will have brown eyes because the brown eye allele is dominant.

Let me know if you have any more questions!