Coalescent trees under recombination and selection.

<p><b>A</b>: Sketch of a neutral coalescent tree with tree size . <b>B</b> and <b>C</b>: A selective sweep in locus C leads to a tree of low height ( small). The selective sweep was initiated by a beneficial mutation at time . At some distance from C, a single lineage (circled branch in C) has “recombined away” leading to the unbalanced tree shown at locus B. Note that tree height between trees B and C changes drastically and that at locus C and at locus B. Multiple recombination events (indicated by the crosses at the bottom line) between loci A and B lead to essentially uncorrelated trees at A and B.