Trees with high frequencies of cherry subtrees (symmetric two-tip configurations) exhibit more symmetric overall tree shapes, whereas trees with low cherry frequencies are more asymmetric. This relationship has been formalized through the connection between the basic reproduction number and cherry frequency in phylogenetic trees. [@colijn_metric_2018]
Definitions
Synthesis
Tree asymmetry, which measures deviation from balanced branching patterns, is established across sources as a fundamental property of tree shape that can be quantified through various structural features including the frequency of symmetric cherry subtrees—pairs of sister tips sharing an immediate common ancestor. The mechanistic relationship appears to operate through the recognition that symmetric configurations like cherries represent local balance within the broader tree topology, with their prevalence inversely related to overall asymmetry measures, and this structural information can be encoded through node labeling schemes that enable metric-based comparisons between trees generated by different stochastic processes. The notes reference a connection between tree asymmetry and the basic reproduction number in epidemiological contexts, suggesting that asymmetry patterns may reflect underlying transmission dynamics, though the specific nature of how cherry frequency mediates or indicates these relationships across evolutionary versus epidemiological trees remains unresolved in the provided material.
Related
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