Biology Reference
In-Depth Information
I
II
a
b
c
d
a
b
c
d
III
IV
a
b
c
d
a
b
c
d
Fig. 13.
Tree III is the strict consensus of trees I and II. Tree IV is the Adams
consensus of trees I and II.
4.5.6. Estimating tree robustness
Because probabilistic methods are based on a probabilistic model, it is
possible to analyze the validity of a result statistically. The ability to do so
is not inherent to the other methods. However, if we make the assump-
tion that all characters evolve independently of each other and that they
all follow the same law of distribution (which need not be known), it is
still possible to apply statistics to their outcome.
Some characters are under more selective pressure than others in
evolution. A mutation in one region of a gene may result in a complete
rearrangement of the three-dimensional structure of a protein; whereas
in another region, it would have a biochemically negligible effect such
as the change of a single amino acid in a loop structure. However, the
correct weighting for characters cannot be known beforehand.
Therefore, a large number of random weighting schemes are tested.
