What specific point mutation in the beta subunit of hemoglobin leads to sickle cell anemia?

• A. A substitution of alanine to glycine at the 6th position.
• B. A substitution of serine to threonine at the 6th position.
• C. A substitution of lysine to arginine at the 6th position.
• D. A substitution of glutamate to valine at the 6th position.

Answer: (D)