In the context of human genetic variation, what type of mutation in the HBB gene causes sickle cell disease?

• A. A chromosomal translocation involving the HBB locus that creates a fusion gene
• B. A missense point mutation (single-nucleotide substitution) that changes a codon and substitutes one amino acid in the beta-globin protein
• C. A frameshift mutation caused by a single-nucleotide insertion that shifts the reading frame of HBB
• D. A nonsense mutation that introduces a premature stop codon in HBB, producing a truncated beta-globin protein

Answer: (B)