Re: How are genes counted in Human Genome Project?
- From: "ErikW" <bryophyta@xxxxxxxxxxx>
- Date: Thu, 12 Oct 2006 13:35:42 -0400 (EDT)
Guy A Hoelzer wrote:
in article egj90t$2p2c$1@xxxxxxxxxxxxxxxxxxx, ErikW at bryophyta@xxxxxxxxxxx
wrote on 10/11/06 10:18 AM:
John Edser wrote:
"ErikW" bryophyta@xxxxxxxxxxx wrote
Perplexed in Peoria wrote:
<drosen0000@xxxxxxxxx> wrote in message
....However, the word "gene" in popular use is ambiguous. It
refers to any one of several different units of hereditary.
It
sometimes refers to the triplet of nucleotides designating an amino
acid,
I've never heard that one. That is usually called a 'codon',
not a 'gene'.
it sometimes refers to a sequence of DNA designating an enzyme
(e.g., Sean Carroll),
The usual definition is a sequence designating a *protein*.
Not all proteins are enzymes. Some have a more structural or
regulatory role.
it sometimes refers to a portion of a chromosome
that particularly resists crossover (e.g., Dawkins),
You have misread Dawkins. He meant a segment small enough so
that crossing over within it is rare. There are no particularly
resistant regions. Dawkins's definition is not an unambiguous
one, but it is useful in thinking about evolution.
and there are
other "genes." Each definition of gene would correspond to a different
size gene and therefore a number of genes in the genome. What type of
gene is being counted in these references to the "Human Genome
Project."?
It is the 'Sean Carroll' one that is used. The reason for the
uncertainty in the count is that a segment may 'look like' it
codes for a protein, but no one has ever seen that protein.
Perhaps it is only produced in the knee-cap (to take a silly example)
and no one has ever studied knee-caps carefully enough. Yet.
JE:-
To be CORRECT any segment that is deemed "one gene" has to code for one
polypeptide and NOT one protein. Almost all proteins are complex
combinations of MORE than just one polypeptide which means that at the very
least MORE than one gene is almost always required to code for ONE protein.
If I understand you correctly then I don't agree at all (concerning
counting genes). Can you give an example?
For example apetala1 has something like 8 exons interrupted by 7
introns all lined up in a row. That would be counted as one gene
whereas you claim it would be 8 if I understand you correctly!?
This is not what John's words say, because those exons do not encode
separate polypeptides. At least that is true for most compartmentalized
genes. The RNAs they produce are usually processed into a single mRNA
prior to translation into a polypeptide.
Well all's well then except that I have no idea what he originally
meant. Is he saying that different genes at different loci form
proteins, and that almost always? Would he call photosystem two to be
one protein? (Sorry to ask you about what JE means. He is of course
welcome to asnwer too.)
Guy
.
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