http://www.bio.net/hypermail/MOLECULAR-EVOLUTION/lost of genes in primate

Jeffrey Mattox jeff at cher.heurikon.com
Sun Mar 3 21:51:34 EST 1996


In article <ralph.1176045731C at 128.196.137.12>,
R M Bernstein <ralph at ccit.arizona.edu> wrote:
>OK, i'll bite: What is an example of an organism that has more _coding_
>sequences but is considered less complex than another comperable organism
>with _less coding_ sequences.

Other than some examples that you could fairly classify as exceptions,
I cannot point to overwhelming evidence that the number of GENES (not
genome size) is uncorrelated with complexity -- so I'll yield to you.
The point of my original comment a few posts back was that the total DNA
content in a genome is unrelated to complexity, and that this phenomenon
is not explained by conventional evolution theory.

From: "Fundamentals of Molecular Evolution," by W-H Li and D Graur, 1991,
Sinauer Associates, Sunderland, MA.

  "The C values in eukaryotes vary from 8.8 x 10^6 bp to 6.9 x 10^11 bp,
   approx. 80,000-fold range.  Unicellular protists, particularly sarcodine
   amoebae, show the greatest variation in C values. The three amniote
   classes (mammals, birds, and reptiles), on the contrary, are exceptional
   among eukaryotes in their small variation in genome size (up to four-fold).
   Other classes, for which a substantial body of C-value data exists, show
   variation of at least 100-fold.

   Interestingly, the huge interspecfic variation in genome sizes among
   eukaryotes seems to bear no relationship to either organismic complexity
   or the likely number of genes encoded by the organism.  For example,
   several unicellular protozoans possess much more DNA than mammals, which
   are presumably more complex.  Moreover, organisms that seem similar in
   complexity (e.g., flies and locusts, onion and lily, paramecium aurelia
   and P. caudatum) exhibit vastly different C values.  This lack of
   correspondence between C values and the presumed amount of genetic
   information contained within genomes has become known in the literature
   as the C-value paradox."

And from "The Cell" (Alberts, Bray, Lewis, Raff, Roberts, & Watson; 3rd
edition, page340):

   Figure 8-6 shows the "Lack of relationship between amount of DNA and
   organism complexity.  The amount of DNA in a haploid genome varies over
   a 100,000-fold range from the smallest procaryotic cell -- the mycoplasma
   -- to the large cells f some plants and amphibia.  Note that the genome
   size of humans is much smaller than that of many organisms that appear
   to be simpler."

Sorry to put up so much -- I guess nobody here is arguing that this
situation does not exist.

Jeff
-- 

Jeffrey Mattox -- jeff at heurikon.com
Cartoon of the day: http://www.heurikon.com



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