Here's why:

* Dominant trait: A dominant trait is expressed even if only one copy of the dominant allele is present.

* Homozygous: An individual with two copies of the same allele (e.g., AA or aa).

* Heterozygous: An individual with two different alleles (e.g., Aa).

Example:

Let's say brown eyes are dominant (B) and blue eyes are recessive (b).

* Homozygous dominant: BB (brown eyes)

* Heterozygous: Bb (brown eyes)

* Homozygous recessive: bb (blue eyes)

As you can see, an individual with brown eyes can have either the genotype BB (homozygous dominant) or Bb (heterozygous). They will express the dominant trait (brown eyes) regardless of whether they have two dominant alleles (BB) or one dominant and one recessive allele (Bb).