Phylogenetics Calculators

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Phylogenetics is the study of the evolutionary relationships among biological entities — organisms, genes, or proteins — and their representation as phylogenetic trees (dendrograms). Trees are constructed from morphological characters or, more commonly today, molecular sequence data (DNA, RNA, protein). Key tree-building methods include distance-based methods (neighbor-joining), maximum parsimony, maximum likelihood (ML), and Bayesian inference. Support values (bootstrap percentages or posterior probabilities) assess how well data support each branch. Phylogenetic trees are used to understand evolutionary history, infer gene function, identify new pathogens, trace disease outbreaks, and guide conservation.

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Phylogenetic Tree Components

  • Root: the common ancestor of all taxa in the tree; inferred from an outgroup
  • Internal nodes: ancestral populations or species; points of divergence
  • Tips (leaves): current taxa (sequences, species); the units being compared
  • Branches: evolutionary lineages; branch length ∝ evolutionary change (substitutions/site)
  • Clade: a monophyletic group — an ancestor and all its descendants

Tree-Building Methods

Neighbor-joining (NJ): fast distance-based; good for large datasets. Maximum parsimony: minimize total mutations; computationally intensive. Maximum likelihood (ML): find tree most likely to produce observed data given a substitution model; statistical standard; IQ-TREE, RAxML. Bayesian inference: MrBayes, BEAST; posterior probability of each clade; most rigorous.

Substitution Models

JC69; K2P (Kimura 2-parameter); HKY; GTR+G. Selected by AIC/BIC using ModelTest-NG or IQ-TREE -m TEST.

Glossary

Phylogenetic Tree
A branching diagram representing evolutionary relationships; tips = current taxa; internal nodes = common ancestors; branch length = evolutionary change; root = most ancient ancestor; clades = monophyletic groups.
Bootstrap Support
% of bootstrap resampled trees containing a given clade; ≥ 70% = adequate support; ≥ 95% = strong support; assesses how well sequence data support each branch.
Maximum Likelihood (ML)
A statistical method finding the tree topology and branch lengths most likely to produce the observed data given a substitution model; the current standard for phylogenetic inference; IQ-TREE and RAxML are widely used.

Frequently Asked Questions

Phylogenetics is the study of evolutionary relationships among organisms, genes, or proteins — represented as branching diagrams called phylogenetic trees. Tree components: Tips (leaves): current taxa being compared (species, sequences). Internal nodes: hypothetical common ancestors — the point where lineages diverged. Branches: evolutionary lineages; length often proportional to amount of change (substitutions per site). Root: the common ancestor of all taxa; requires an outgroup to determine. Topology: the branching pattern. The tree shows which groups are most closely related — a clade is a monophyletic group (one ancestor + all its descendants).

Distance methods (Neighbor-Joining, NJ): calculate pairwise evolutionary distances between all sequences; build a tree by grouping nearest sequences; fast; appropriate for large datasets. Maximum Parsimony (MP): find the tree requiring the fewest evolutionary changes to explain the observed sequence data; computationally intensive; not commonly used today. Maximum Likelihood (ML): find the tree topology and branch lengths that maximize the probability of observing the data given a substitution model; the current statistical standard; IQ-TREE and RAxML are widely used implementations. Bayesian Inference (BI): MrBayes, BEAST; calculates posterior probability of each tree given the data; most statistically rigorous; provides uncertainty quantification.

Bootstrap analysis: a resampling method to assess confidence in tree topology. Procedure: randomly resample columns from the alignment with replacement → 100–1,000 bootstrap replicates → build a tree from each → count the % of bootstrap trees that contain each clade in the best tree. Interpretation: Bootstrap ≥ 70%: generally considered adequate support; ≥ 95%: strong support. Some researchers prefer Bayesian posterior probabilities (BPP): BPP ≥ 0.95 is strong support (equivalent to bootstrap ≥ 95%). Low bootstrap (< 50%): insufficient data to confidently resolve that branch; the true relationship is uncertain. Note: bootstrap is conservative — it can underestimate true confidence.

A substitution model describes the process of nucleotide or amino acid change over time — the probabilities of each type of substitution occurring. Common DNA models: JC69: equal rates; equal base frequencies. K2P (Kimura 2-parameter): different rates for transitions (A↔G, C↔T) and transversions; equal base frequencies. HKY85: K2P + unequal base frequencies. GTR (General Time Reversible): 6 rate parameters + 4 base frequencies; most general; most accurate for most datasets. +G: gamma distribution for rate variation across sites. Model selection: use AIC or BIC (jModelTest, ModelTest-NG, IQ-TREE -m TEST) to choose the best model. Wrong model → biased branch lengths and topology.