Following the coronavirus’s spread through the population — and anticipating its next move — is an important part of the public health response to the new disease, especially since containment is our only defense so far.
Just looking at an infected person doesn’t tell you where their version of the coronavirus came from, and SARS-CoV-2 doesn’t have a bar code you can scan to allow you to track its travel history. However, its genetic sequence is almost as good for providing some insight into where the virus has been.
An organism’s genome is its complete genetic instructions. You can think of a genome as a book, containing words made up of letters. Each “letter” in the genome is a molecule called a nucleotide — in shorthand, an A, G, C, T or U.
Mutations can occur every time the virus replicates its genome, so that over time mutations accumulate in the viral genome. For example, in place of the “word” CAT, the new virus has GAT. The virus carries these minor modifications as it moves from one person to the next host.
