Sickle cell anemia is caused by a point mutation, specifically a missense mutation in the beta-globin (HBB) gene that changes one amino acid in the hemoglobin protein.

Quick Scoop: The Exact Mutation

  • It’s a single nucleotide substitution (a point mutation) in the DNA of the HBB gene.
  • At codon 6 of the beta-globin chain, the DNA changes from A to T, converting the codon from GAG (glutamic acid) to GTG (valine).
  • Because one amino acid (glutamic acid) is replaced by another (valine), this is called a missense mutation.
  • The abnormal hemoglobin produced is called hemoglobin S (HbS).

In simple exam language

If you need a short, exam-style answer to “what type of mutation is sickle cell anemia?” you can write:

Sickle cell anemia is caused by a point (missense) mutation in the beta- globin gene, where glutamic acid at position 6 is replaced by valine (GAG → GTG), producing hemoglobin S.

Why that tiny change matters

  • Normal hemoglobin (HbA) keeps red blood cells soft and round so they flow easily.
  • Hemoglobin S tends to stick together when oxygen is low, making red blood cells stiff and sickle-shaped.
  • These sickled cells can block small blood vessels, leading to pain crises, anemia, and organ damage.

Inheritance angle (bonus for genetics questions)

  • A person gets sickle cell anemia when they inherit two copies of the mutant HBB gene (HbS), one from each parent.
  • People with only one copy (AS) usually have the sickle cell trait , not full-blown disease, but can pass the allele on.

TL;DR: The answer they’re usually looking for is: a point mutation (missense) in the beta-globin gene causing a Glu→Val substitution at position 6, forming hemoglobin S.

Information gathered from public forums or data available on the internet and portrayed here.