In which gene does point mutation occur in sickle cell anemia?

Sickle cell anemia:

1. It is an autosomal blood disorder that is caused by codominant alleles.
2. The normal allele of hemoglobin is Hb^A.
3. Persons suffering from sickle cell anemia have the gene Hb^S.
4. Persons having Hb^A/Hb^A genotype have normal hemoglobin while people having Hb^S/Hb^S suffer from sickle cell hemoglobin.
5. The gene Hb^S is located on the 11^th chromosome and produces abnormal hemoglobin.
6. It is different from normal hemoglobin in its oxygen-carrying capacity.
7. The low concentration of hemoglobin makes the hemoglobin carrying the mutant gene narrow and sickle-shaped.
8. The RBCs clump together causing vascular obstruction and severe anemia which damages the vital organs like the spleen, liver, and brain.
9. Normal hemoglobin differs from abnormal hemoglobin in only one amino acid at the $\beta$chain.
10. The 6th amino acid in the $\beta$chain of hemoglobin is glutamic acid which is replaced by valine in abnormal hemoglobin.