Bifurcated subtrees.

Patterns on a tree can be described in terms of natural variables, or elemental components, examples of which are shown here. Each component is a bifurcated pattern centered on a subtree (ℓ, τ) and expressed in a generation g (where τ is ignored in an unordered tree). For example, the blue/non-blue bifurcated pattern occupies a subtree rooted at ℓ = 3 and observed at generations 5, 6, and 7. Note that ℓ = 1 variation (on the right) is a bifurcation across the whole pedigree. Variation among different pedigrees would be labeled with ℓ = 0.