Answer:
POINT MUTATION (SUBSTITUTION)
Step-by-step explanation:
A point mutation is that mutation which involves only one nucleotide base. Point mutation can, however, occur in different ways such as SUBSTITUTION. Substitution point mutation is that which involves the replacement of a single nucleotide base by another in a gene sequence.
This is the case in this question regarding the mutation that causes sickle cell anaemia. According to this question, Sickle cell anemia is a disease that occurs when a mutation in the base pair of the hemoglobin beta gene causes a SINGLE replacement of GLUTAMIC ACID (Glu) by VALINE (Val). This shows that it is a type of SUBSTITUTION POINT MUTATION.