With the birth of a child, it gets its genes from both parents. Some genes 'override' other genes. Using hair color as example:

If one parent is blond (Pb) and one parent is black hair (Pd), blond would be the recessive gene, and dark would be the dominant gene. Meaning:

Pb x Pb = Blond Pd x Pd = Dark Pb x Pd = Dark Pd x Pb = Dark

Recessive genes occur in the genotype (inside the body, disease, disorder) or fenotype (appearance, blue eyes brown eyes). In all other cases, the dominant gene will override the recessive gene.