Most coalescent events for a sample of lineages occur in the recent past with only a few lineages having long times to coalescence.

• The effective population size (Ne) can be defined for lineage branching models by reference to the probability of two randomly sampled gene copies descending from the same ancestral copy. This probability decreases as the effective size of populations grows larger. The coalescent model leads to definitions of the inbreeding effective population size that are identical to those obtained using autozygosity.

• Exponential population growth changes the distribution of coalescence times relative to a population with constant population size. When population size is growing, lineages nearest the present tend to have the longest coalescence waiting times because the probability of coalescence grows steadily smaller toward the present. When population size is shrinking rapidly, the probability of coalescence grows steadily greater toward the present causing lineages nearest the present to have the shortest coalescence waiting times.

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