Answer: Two alleles for mutated haemoglobin is required to have sickle cell disease
Explanation: Sickle cell disease is a genetic disorder in which an individual inherits two allele for sickled haemoglobin from the parents. Every trait is controlled by a pair of gene, one gene from each parent. For an individual to have sickle cell disease he must have two alleles for the mutated haemoglobin, one from each parent. Haemoglobin is a protein found in the red blood cells that binds and transports oxygen to the cells. Haemoglobin is a protein with four subunits: two alpha chains and two beta chains. In a mutated haemoglobin, valine replaces glutamate at position six of the two beta chains. This point mutation on the beta chains of haemoglobin causes the aggregation of haemoglobin, thus giving the red blood cells a sickle shape instead of a disc shape of normal haemoglobin. The allele for the sickle haemoglobin is represented as S and for an individual to have sickle cell disease, he or she must inherit one allele from each parent.
