Here's how it works:

* Alleles: Genes come in different versions called alleles. You inherit one allele from each parent.

* Dominant Allele: A dominant allele (often represented with a capital letter, like "B") expresses its trait even if only one copy is present.

* Recessive Allele: A recessive allele (often represented with a lowercase letter, like "b") only expresses its trait if two copies are present.

Example:

* Brown Eyes: The allele for brown eyes (B) is dominant over the allele for blue eyes (b).

* Possible Genotypes:

* BB: Brown eyes (two dominant alleles)

* Bb: Brown eyes (one dominant and one recessive allele)

* bb: Blue eyes (two recessive alleles)

In the case of complete dominance, an individual with one dominant allele (Bb) will have the same phenotype (brown eyes) as an individual with two dominant alleles (BB). The recessive allele is completely masked.