In article <43cdoq$71f at studium.student.umu.se>,
Agneta.Guillemot at historia.umu.se (Ludvig Mortberg) wrote:
> Evolution is descent by modification. There is no constant clock
> in the genom that makes it possible to deduce relationships in
> organisms just by comparing genes and seeing which sequences
> are most similar. You must look at what is unique. You must have
> outgroups and use charachters of high information value such as
> morphologic traits, whole genes etc. The information value of a
> single nucleotide substitution isn't very high.
Like so often the truth lies somewhere in between. While I am weary of
people that rely blindly and exclusively on numbercrunching these methods
have generated reliable and invaluable data. I would like to amplify on
one short sentence above: >You must look at what is unique.<
You are absolutely right, that this is one of the best ways to establish
phylogenetic relationships. Molecular Biology has given us the great
opportunity to look at such novelties in genomes in the form of repetitive
elements (e.g. SINEs, retrogenes, L1 retroelements) or newly arisen genes
(via recombination or retroposition). N. Okada (Curr. Opin. Genet. Dev. 1,
498-504; 1991) calls such sequences :time-landmarks of evolution:
For other examples see: P.P. Minghetti and A. Dugaiczyk (1993) PNAS
90, 1872-1876 and J.A. Martignetti and J. Brosius (1993) PNAS 90,
9698-9702 and references therein.
Regards,
Juergen
