Phylogeny
A pylogeny tree is a hierarchy of “leaf” elements, based on their similarity. In biology, the phylogeny often refers to an ancestral, evolutionary hierarchy. The biological tree of life is one example. Virus variants are another, faster-moving example.
Key Assumptions
There are a few assumptions taken to assemble phylogenies.
- Trees model the phylogeny. All leaves can connect to each other, and there can be no cycles 1.
- The leaf nodes may be observable, but the ancestors are not assumed not to be.
- With Distance-based phylogeny, some form of distance can be measured among the leaf nodes.
- With Alignment-based phylogeny, a DNA/RNA sequence from a multiple-alignment corresponds to each node in the tree, and the edge weights correspond to string distances (mutations) among each leaf.
Types
A tree may be:
- Unrooted or rooted.
- Bifurcate or multifurcate.
A cycle in a phylogeny “graph” implies a species/variant that exists today could become its own (perhaps indirect) parent. Perhaps time travel will not rule out this possibility. ↩︎