When an extra base is added to an organism's DNA, the mutation is known as an insertion.

Here's why:

* Insertion: This refers to the addition of one or more nucleotide bases into an existing DNA sequence. This disrupts the normal reading frame of the DNA, often leading to a frameshift mutation.

* Deletion: This refers to the removal of one or more nucleotide bases from an existing DNA sequence. Like insertions, deletions can also cause frameshift mutations.

Let me know if you have any other questions about mutations!