Transitions are types of DNA mutations. They are places in your DNA where nucleotides (Cytosine, Guanine, Adenine, and Thymine) have changed value.

Transitions are where a purine has mutated to the complimentary purine (A <-> G) or where a pyrimidine has mutated to the complimentary pyrimidine (C <-> T). Transitions are shown by giving the original value capitalized before the location and the mutated value capitalized after the location. Thus, a transition of a C nucleotide at locus 146 to a T is shown as C146T.