To calculate the lengths of non-terminal branches, branch swapping
is used on them.
Branch swapping (aka NNI=Nearest Neighborhood Interchange) is the most
atomic operation possible at an inner branch and has as such an effect on
the overall costs of the tree.
That effect is used as branchlength of the inner branch.
The branchlength reflects the significance of the branch, i.e.
-
the exact topology around SHORT inner branches has little influence
on the overall tree costs, i.e. the calculated topology does most
likely NOT reflect the "real phylogentic topology".
-
Opposed, the exact topology around LONG inner branches has big influence
on the overall tree costs, i.e. the calculated topology does most
likely reflect the "real phylogentic topology".
|