What type of mutation causes sickle-cell anemia? -nonsense mutation
-chromosomal mutation
-silent mutation
-missense mutation

Sickle cell anemia is caused by a missense mutation.

Explanation:

In sickle cell anemia, a change in the DNA nucleotide sequence is observed, where adenine is substituted by thymine, whose expression is the change in the sequence of amino acids in β-globin, with valine being incorporated instead of glutamic acid. This constitutes a mutation of the missense type.

Missense mutations are characterized by the substitution of one nucleotide by another in the DNA sequence —a point mutation— whose consequence is reflected in the transcription and substitution of one amino acid by another in a protein, whose structure or function will be altered.

The change from glutamic acid to valine in β-globin causes an altered hemoglobin, giving the abnormal erythrocytes observed in sickle cell disease.