FIGURE 2.
Haplotype blocks defined through identity by descent (IBD). Panels (a) and (b) show the same 11 hypothetical DNA sequences depicted as horizontal lines. The trees on the left and right sides show the genealogy for the set of sequences on either side of a recombination event (indicated by the vertical black line); the light grey branch in both trees shows how the effect of recombination changes the structure of the genealogy on either side. Mutations are shown as symbols that correspond to the branches upon which they arose. Under the IBD definition, haplotype blocks can be defined based on DNA segments that derive from a given set of ancestors, shown here by the coloured sections of branch and DNA sequence. The only difference between panels (a) and (b) is that these ancestors are defined at two different arbitrary time points, Ta and Tb, yielding different haplotype structure