DNA is composed of four nucleotide bases:

* Adenine (A)

* Thymine (T)

* Guanine (G)

* Cytosine (C)

Mutations can occur in various ways, but they all involve alterations to the sequence of these bases within the DNA molecule. These changes can involve:

* Substitution: One base is replaced with another (e.g., A replaced with G).

* Insertion: An extra base is added to the sequence.

* Deletion: A base is removed from the sequence.

These alterations in the DNA sequence can have various effects on the protein coded by the gene, ranging from no effect to a complete loss of function.