A: Sequencing of representative isolates to create a phylogenetic tree of a coronavirus. B: Tracing a pandemic pathway. Specific viral isolates are sequenced to detect mutation and thereby reconstruct the chain of transmission.

In panel B, each circle represents a coronavirus isolated from a patient. Different colors indicate a virus mutation. A genome sequencer device (machines in the figure) is used to determine the location and type of mutation: AUUU, a segment of the viral genome Adenine Uracil Uracil Uracil; AUCU, same segment of the genome after mutation Cytosine replacing middle Uracil; or GUCU, same segment of the genome following another mutation: Guanine replaced Adenine.