A son cannot inherit the defective gene from his father.

People who have only one defective gene are known as carriers.

These individuals do not develop the disease but they can pass the defective gene on to their own children.

You must get a copy of the defective gene from both your parents to have the disease.

A person with one defective gene is called a "carrier."

Only one defective gene is needed to cause the condition, which can be passed from either parent to both boys and girls.

They could still pass the defective gene to their own children, though.

For a child to be affected, both parents must carry the defective gene.

People are born with the defective gene, but symptoms usually don't appear until middle age.

This means you don't have the disease but can pass the defective gene to your child.