How do people get hemophilia? (Level 1)

Your eye color, hair color and texture, skin color and many of your facial features - including the shape of your nose - are physical characteristics inherited from your parents. As you grew into a baby inside your mother, you were created with special cells from your father and cells from your mother. These cells had chemical "directions" in them that told your body exactly how to develop into a baby. Because some of these cells were from your father, his directions might have told you to have blue eyes like him. Or, because some of the cells were from your mother, you might have received directions to have the same curly hair as she, not the straight hair of your father. The possible combinations of the characteristics you can inherit are endless!

Guess what else can be inherited? Diseases and physical disorders. Hemophilia is a disorder that can be inherited. It can be inherited from the mother.

A mother who can pass hemophilia along to her baby is called a carrier. This means that inside her cells she carries directions for blood clotting that are scrambled, although her blood knows how to clot correctly. When her baby inherits the cells with the scrambled directions, the baby's body cannot "read" the directions and his blood cannot clot. This is known as hemophilia.

If the mother who is a carrier had several baby boys, it's possible that some might not have hemophilia. Sometimes the scrambled directions are passed along; sometimes they are not. Each time the mother is pregnant with a son, it is like a flip of a coin: heads, she has a boy with hemophilia; tails, she does not. Each flip of a coin has a 50% chance of coming up heads or tails.

If the mother is a carrier and the father does not have hemophilia, their daughters have a 50% chance of being a carrier. They will not have hemophilia, but they may have children with hemophilia.

Pretend that you just bought a new CD player. Just as you were about to assemble it, you discovered that the store sent directions that were half in English and half in Greek! You cannot read them! You can't follow the directions to complete the job! When a person inherits hemophilia, he receives directions for blood clotting that are mixed up chemically. His body cannot read them, and cannot clot blood properly.