When comparing the amino acid sequence of normal hemoglobin and sickle cell all are the same except the type your answer codon of HbS, in which and type your answer...
in normal HbA has been substituted for a type your answer
This change makes the 6th amino acid type your answer...
in Hbs while HbA has the amino acid type your answer
This change alters the shape of the hemoglobin type your answer
resulting in Sickle cell anemia. This type of mutation is called a substitution or point mutation