[Taxacom] Taxacom Digest, Vol 58, Issue 13

[Sergio Vargas]

  Hi,

>  Unfortunately, with DNA sequence data, one has to build the tree before being able to identify the
>  putatively uniquely shared similarities since there is no way to do this beforehand for each character>  since there are only four characters that replace each other rather than different character states as>  in morphogenetics.


I don't get this.

Why is not possible to propose "uniquely shared similarities" from 
sequence data?

Imagine you have 3 protein coding orthologous sequences with no gaps (to 
avoid alignment sensitivity) belonging to three spp. Why is not possible 
to establish that sp A and sp B share an A (or a His if you use 
aminoacids) in position 35 of the sequence, or better say why is not 
possible to treat this as an "uniquely shared similarity" before the 
analysis?

thanks

sergio