Question: what is the mutation of sickle cell anemia

title: Sickle cell disease
text: Sickle cell disease occurs when a person inherits two abnormal copies of the haemoglobin gene , one from each parent . This gene occurs in chromosome 11 . Several subtypes exist , depending on the exact mutation in each haemoglobin gene . An attack can be set off by temperature changes , stress , dehydration and high altitude . A person with a single abnormal copy does not usually have symptoms and is said to have sickle cell trait . Such people are also referred to as carriers . Diagnosis is by a blood test , and some countries test all babies at birth for the disease . Diagnosis is also possible during pregnancy .