Your body is built from instructions. Every cell in your body — from your skin to your liver to your blood — was shaped by a set of biological instructions inherited from your parents. These instructions are called genes, and the combination you carry is your genotype. When people in Nigeria talk about genotype, they are usually referring specifically to haemoglobin genotype — the genetic code that determines the type of haemoglobin your red blood cells carry. Haemoglobin is the protein inside red blood cells that carries oxygen around your body. The type you have affects how your blood functions. There are four main haemoglobin genotypes you need to know: AA — You have two copies of the normal haemoglobin gene. Your red blood cells are healthy and round, and they function the way they should. This is the most protective genotype. AS — You have one copy of the normal gene and one copy of the sickle cell gene. You are a carrier. You will not develop sickle cell disease yourself, but you can pass the sickle gene on to your children. SS — You have two copies of the sickle cell gene. This means you have sickle cell disease, a serious condition that affects how your red blood cells carry oxygen and causes episodes of severe pain, among other complications. AC — You have one normal gene and one copy of the haemoglobin C gene. Like AS, you are a carrier. On its own this causes few problems, but it becomes significant in terms of what you can pass to your children. There are also rarer types like SC and CC, but AA, AS, SS, and AC are the most common in Nigeria. Knowing your genotype is not a medical luxury. It is basic knowledge about who you are.