It happens because of Point mutation
Step-by-step explanation:
A point mutation can be understood as when one nucleotide is added, deleted or changed. Through change in DNA structure a gene can be altered and it is called mutation. Point mutation’s other term is insertion as well as deletion. It mostly involves in substitution.
Rarely, Point mutation is responsible for huge change. Basically, two types of point mutation happen. They are transition or transversion mutations.