Here's why:

* Heterozygous means having two different alleles for a particular trait.

* Dominant allele is an allele that expresses its trait even if only one copy is present. It is represented by a capital letter (e.g., "B").

* Recessive allele is an allele that only expresses its trait if two copies are present. It is represented by a lowercase letter (e.g., "b").

So, a heterozygous trait would be represented by a combination like Bb. The dominant allele (B) masks the recessive allele (b), meaning the individual will express the trait associated with the dominant allele.