Some differences or abnormalities in our chromosomes or genes come to us via our parents' reproductive cells. In other words the variation is present in the egg and/or sperm cell and is therefore transferred to all our cells.
As an embryo we develop from these two parental reproductive cells (the egg cell and sperm cell), which multiply after merging (fertilization) through cell division and specialise further to form a new organism. That is the basis of our inheritance: it explains why we resemble our parents and other family members - because each family has its own specific genetic variations - and also why we sometimes inherit specific disorders. We describe these disorders and diseases as congenital or inherited disorders.