Final answer:
Sickle-cell anemia results from a single base change in the β-globin gene that causes a single amino acid substitution in the beta chain of hemoglobin, leading to red blood cells with an abnormal sickle shape.
Step-by-step explanation:
Sickle-cell anemia is caused by a mutation in the β-globin gene. This mutation is a single base change from a normal allele, which leads to the production of abnormal hemoglobin. The pathway from DNA to functional hemoglobin involves the specific sequencing of amino acids in the protein chain, and a mutation in the DNA sequence can change this.
Specifically, in sickle-cell anemia, the mutation causes a single amino acid substitution in the beta chain of hemoglobin. This alteration causes erythrocytes, or red blood cells, to take on a sickle or crescent shape. As a result, these abnormal cells can obstruct capillary flow and inhibit oxygen delivery within the body, manifesting in the symptoms associated with sickle-cell anemia, such as painful episodes and potential organ damage.