Relationship between sequence conservation, Ups group, and frequency in the data set for each domain subclass.

<p>Each dot represents a domain subclass, as classified by Rask <i>et al. </i><a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002451#pcbi.1002451-Rask1" target="_blank">[25]</a>, with the colour of the dot representing the association of that subclass with Ups group (yellow dots are only found in UpsA <i>var</i> genes, dark green dots are only found in UpsB or C <i>var</i> genes, and intermediate colours are found in all Ups groups in various proportions). <b>Inset: Hypothetical population distribution of </b><b><i>var</i></b><b> genes.</b> It has been suggested that UpsA <i>var</i> genes are more conserved because they are optimized for functionality in naïve individuals, whereas UpsB and C <i>var</i> genes are more prevalent (both in the population and within <i>var</i> gene repertoires) but more diverse and can sustain infection in individuals with previous exposure <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002451#pcbi.1002451-Bull3" target="_blank">[21]</a>. This would lead to a hypothetical distribution of genes that follows a similar pattern to the domain subclasses observed here. Note that pregnancy associated malaria <i>var</i> genes (denoted ‘pam’ in the figure) represent an extreme case of this pattern.