Sickle cell аnemiа is аn autоsоmal recessive disease caused by a mutatiоn in the gene that encodes the hemoglobin protein. Homozygous mutations in this gene lead to the production of mutant hemoglobin protein. When only mutant hemoglobin protein is produced, red blood cells (RBCs) adopt an abnormal sickle shape and their function is impaired. On December 8, 2023 the FDA approved Casgevy to treat sickle cell anemia. Casgevy is the first medical use of the CRISPR-Cas gene-editing system. Casgevy uses CRISPR-Cas9 technology to cut a gene in the genome. What gene is targeted by the Cas9 used in Casgevy?