A point mutation is a single base substitution. In a point mutation, one base is substituted for a different base.
Point mutations can be classed as either transitions or transversions depending on the class of base that is substituted.
A transition substitution is the swapping of one purine (adenine or guanine) with another, or one pyrimidine (cytosine or thymine) with another.
Transitions are more common than transversions as they occur between bases of a similar structure.
- A transversion substitution involves the exchange of a purine base for a pyrimidine base or vice versa.