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Any comments?

Ludvig Mortberg Agneta.Guillemot at historia.umu.se
Thu Oct 19 03:49:35 EST 1995


>All the data demonstrate 
>that archaebacteria are more closely related to 
>eubacteria than to eukaryota, thus supporting tha 
>classical division of living organisms into two main 
>superkingdoms, Prokaryota and Eukaryota.


>Their seperate, reciprocally rooted trees 
>for elongation factors and ATPase subunits  
>showed Bacteria (eubacteria) as branching first from the 
>universal tree with Archaea (archaebacteria) and 
>Eukarya (eukaryotes) as sister groups. 

Who do you belive, and why? More studies? But how many?

The idea that there is something inherrently wrong with the
method has to be considered!

The two "wrongs" are as follows:

(1) A "close distance" between proteins or DNA sequences does not
always reflect close relationship (within an organim and between
organims). That is because mutations accumulate at different speeds at
different loci at different times in the history of an organim.
Selective pressure differs from time to time etc. To put it shortly;
proteins etc., can be more similar in distantly related species than
in closely related ones (and vice versa).

(2) When a cladistic approach is used, "shared derived
sequences/mutations" have been found that apparently could be used in
a cladogram. The problem is that of information content. A cladogram
with morphologic characters should not be put aside for one where the
characters are a few nucleotide substitutions.

L.

In next issue: Whales - traditional classification overturned by
molecular systematics. Also the case of the giant panda.








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