while the chance that the event is a coalescence is k(k - 1) 2

Using the cumulative exponential distribution specified by equation 5.44 and then determining whether each event is a mutation or a coalescence, it is possible to construct a coalescent genealogy that includes the possibility of mutations occurring along each branch (Fig. 5.13).

The pattern of mutations on genealogical trees has some general features. Since the chance of mutation is assumed to be constant through time, the more time that passes, the greater the chance that a mutation occurs. This means that longer branches tend to experience more of the mutations on average in genealogical trees, while shorter branches are less likely to exhibit mutations. Recall the metaphor of branch length as a road that was used in Chapter 3 to describe the total branch length of a genealogy. If mutations are road signs with a constant chance of appearing per distance of roadway, then longer stretches of road are expected to


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