What is an mtDNA insertion? What is the nomenclature for displaying them?

Insertions are types of DNA mutations. They are places in your DNA where nucleotides (Cytosine, Guanine, Adenine, and Thymine) have been added to the DNA sequence.

In in the example below, the sequence has an insertion at position 309. An insertion is denoted by a .1. The nucleotide added is Cytosine, therefore denoted with a C. The insertion then looks like this: 309.1C.

A site may have consecutive insertions.

If you have a two-nucleotide insertion, we show the result like this: 309.1C, 309.2C. It indicates that two extra copies of Cytosine have been inserted at position 309.