Thalassemia is an example of

The correct option is B Frame shift mutation
The gene mutations that alter the base sequence of the whole genetic frame from the point of the mutation are called frame shift mutations.

A transition is the substitution of one type of base by other of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with a pyrimidine (cytosine to thymine/uracil and vice versa) only.

Substitution of purine base for a pyrimidine base or substitution of pyrimidine base for a purine base is called as transversion.

Mutation in single nucleotide base of a DNA segment is called as the point mutation.

Rearrangement of the chromosomal segment between two non-homologous chromosomes is called as translocation.

Thalassemia is a group of blood disorders which are caused by mutations in the HbB and HbA genes present on chromosome 11 and chromosome 16 respectively. The unequal crossover within globin gene complexes causes deletion which in turn leads to backward shifting of the reading frame. Thus, the disease is caused by a frameshift mutation.

So, the correct answer is option B.