Cladistic methods
rely on assumptions about ancestral
relationships as well as on
current data.
Within the field of taxonomy there are two different methods and
philosophies of building phylogenetic trees: cladistic and phenetic.
Cladistic vs.
Phenetic
Phenetic methods
construct trees (phenograms) by
considering the current states
of characters without regard to the evolutionary
history that brought the species
to their current phenotypes.
•For character data
about the physical traits of organisms (such as
morphology of organs etc.) and for deeper
levels of taxonomy, the cladistic approach is almost
certainly superior.
•Cladistic methods are often
difficult to implement with molecular
data because all of the assumptions are
generally not satisfied.
•Computer algorithms
based on the phenetic model rely on Distance Methods to build of trees from sequence
data.
•Phenetic methods count each
base of sequence difference equally, so a single event
that creates a large change in sequence
(insertion/deletion or recombination) will
move two sequences far apart on the final
tree.
•Phenetic approaches
generally lead to faster algorithms and they
often have nicer statistical properties for
molecular data.
•The phenetic approach is popular
with molecular evolutionists because it relies heavily
on objective character data (such as
sequences) and it requires relatively few assumptions.
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