Effective population size and time to most recent common ancestor for HIV-1 subtype A1 and A6.

Bayesian Skyline plot, based on a ‘relaxed clock’ coalescent framework analysis, was constructed using 231 sequences (representing all years and countries). X-axis represents time in years, while Y-axis shows the effective population size. The thick blue line and solid grid (blue) represents mean 95% lower posterior density (HPD) intervals. The tMRCA of HIV-1 subtype A1 and A6 are indicated with red boxed arrows. Pink, light blue and green shaded areas represent the period of increase in viral effective population size, decline and plateau phase, respectively.