What type of trait is always expressed when present?

A dominant trait is a characteristic that will always be expressed in an organism if at least one allele for that trait is present in its genetic makeup. In genetics, traits are determined by alleles, which can be dominant or recessive. A dominant allele masks the effect of a recessive allele when both are present, ensuring that the phenotype (the observable traits) associated with the dominant allele is the one that is expressed.

In contrast, recessive traits only manifest in an organism if two copies of the recessive allele are present and no dominant allele is present to suppress it. Heterozygous refers to a situation where an individual has two different alleles for a trait, which means that one may be dominant and the other recessive. Phenotypic pertains to the physical expression of traits and does not specify dominance or recessiveness.

Therefore, the defining characteristic of dominance in genetics is that it guarantees expression when present, making it the correct answer.