What genetic disorder is an example of a point mutation?

Sickle cell anemia is indeed an example of a point mutation. This condition arises from a single nucleotide substitution in the beta-globin gene, where adenine (A) is replaced by thymine (T). This subtle change results in the alteration of one amino acid in the hemoglobin protein—specifically, it changes glutamic acid to valine. This seemingly minor modification has significant consequences for the structure and function of hemoglobin, leading to the characteristic sickling of red blood cells in affected individuals.

In contrast, cystic fibrosis is typically caused by a deletion of three nucleotides in the CFTR gene, which results in the loss of a phenylalanine residue, rather than a point mutation. Turner syndrome and Down syndrome are chromosomal abnormalities where the entire chromosomes are affected—Turner syndrome involves a missing X chromosome, while Down syndrome results from an extra copy of chromosome 21 (trisomy 21). Thus, the nature of the mutations in these conditions distinctly differs from the point mutation found in sickle cell anemia.