Download Phylogenetic tree factsheet

Phylogenetic tree factsheet
A phylogenetic tree is a visual representation of the relatedness of species by descent from a
common ancestor.
Phylogenetic tree - The root of
the tree represents the ancestral
lineage,the branch tips
represent existing species, the
branches connect common
ancestor and the nodes depict
where one species converged
into two or more species.
Because the fossil record is incomplete and we do not have all evolutionary history, we have to
infer some things from data. For example, homologous structures (those that are derived from the
same body part in a common ancestor) can be examined. Feathers of modern birds are homologous
with feathers found in fossils. In contrast, the wings of birds and insects are analogous (derived from
different ancestral structures).
The aim of tree building is to identify and represent shared derived traits accurately. Species
that share derived characters belong to a clade. A derived character shared by a clade is called a
synapomorphy of that clade (for example if all species in that clade are with tails).
One of the most basic ways to distinguish between ancestral and derived traits is by out-group
analysis. In this approach traits of the group being studied - the in-group - are compared to traits of a very
close relative that clearly branched off earlier - the out-group.
NOTE: In the 1970’s researchers began to use molecular characterstics (such as DNA, rhibozomal RNA)
to construct phylogenetic tree. This has revolutionised phylogenetics and in some cases caused
existing phylogenetic trees to be rearranged.