... generation.¹

An important assumption of the coalescent is that populations are large enough that we can ignore the possibility that there is more than one coalescent event in a single generation. We also only allow coalescence between a pair of alleles, not three or more. In both ways the mathematical model of the process differs from the diagram in Figure 1.

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... is,²

Though you may not remember it.

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... that.³

Remember that we're counting generations backward in time, so when I say that a coalescent event occurred at time $t$ I mean that it occurred $t$ generations ago.

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....⁴

If you've had a little bit of probability theory, you'll notice that equation 1 shows that the coalescence time is a geometric random variable.

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... alleles.⁵

Okay, okay. What I should really have said is ``It's not too hard to extend this approach to multiple alleles.''

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... follows⁶

Using logic just like what we used in the two allele case.

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... is⁷

If you don't see why, don't worry about it. You can ask if you really care. We only care about $\bar t$ for what follows anyway.

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