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Re: 25000 genes


Meum71@aol.com wrote:
RE:>>I do not know if we can make these kinda of "guesses" and expect them to be

accrete.  For along time scientists said humans had 100,000 genes, but it turns
out we
only have 30,000.

Ah yes, the old assumptive leap gets us into trouble all to frequently.
However, if Ben were pegging the number of bp's, then I presume we could fairly
quickly reach consensus.  What we don't know by using gross assessments is the
density of the genes or the sequences of the bases and peptides.   And we don't
know which genes are involved in making one species or another particularly
susceptible to this disease or that one.

It seems likely that as the amount of research escalates, the cost/benefit ratio
will improve dramatically as well.

I found the following comment about Arabidopsis quite intriguing.  I quote from
Nature, 14 Dec 2000, pg 801:

"What does the duplication in the Arabidopsis genome tell us about the ancestry
of the species?  Polyploidy occurs widely in plants and is proposed to be a key
factor in evolution.  As the majority of the Arabidopsis genome is represented
in duplicated (but not triplicated) segments, it appears most likely that
Arabidopsis, like maize, had a tetraploid ancestor.  A comparative sequence
analysis of Arabidopsis and tomato estimated that a duplication occurred ~112Myr
ago to form a tetraploid.  The degrees of conservation of the duplicated
segments might be due to divergence from an ancestral autotretraploid form, or
might reflect differences present in an allotetraploid ancestor.  It is also
possible, however, that several independent segmental duplication events took
place instead of tetraploid formation and stabalization".

"The diploid genetics of Arabidopsis and the extensive divergence of the
duplicated segments have masked its evolutionary history.  The determination of
Arabidopsis gene functions must therefore be pursued with the potential for
functional redundancy taken into account.  The long period of time over which
genome stabilization has occurred has, however, provided ample opportunity for
the divergence of the functions of genes that arose from duplications".

Which leads to the question, "How does one know with certainty that the Blue
Color in Hosta is controlled by but one gene"?  And like I said, I need to
review Ben's presentation because I'm sure I did not comprehend quite a bit
(haven't taken genetics EVER, let alone in high school).  I'm not "challenging
the hypothesis" but I am simply wanting to understand the conclusions drawn a
bit better.  With up to six different kinds of wax involved with the Blue color,
perhaps there are more genes involved?

So little time, so many questions....

Andrew L.





> In a message dated 02/14/2001 2:54:35 AM Central Standard Time,
> zonneveld@RULBIM.Leidenuniv.nl writes:
>
> << additional information on this.""
>  I determine the amount of DNA in pg (= 10 to the minus 12 gram)
>  1pg is 10 to the 9 basepairs so it is easy to calculate how many
>  basepairs there are in a hosta with say 20 pg of DNA The number
>  of genes in hosta is probably not much different from any other
>  plant The number of genes in Arabidopsis has been determined at
>  25000 So my guess for Hosta was pretty close!
>   >>
>
> I do not know if we can make these kinda of "guesses" and expect them to be
> accrete.
>
> For along time scientists said humans had 100,000 genes, but it turns out we
> only have 30,000.
>
> Plants have more complicated genomes than most animals and I would not assume
> the number of functional genes of any plant.  Especially one that has evolved
> from redundant chromosomes.
>
> Paul
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