Re: DNA sequencing

On Apr 25, 6:42 pm, "rmj" <gle...@xxxxxxx> wrote:
Does anyone know of any web site that goes into detail regarding the
methodology of sequencing DNA?
I can't imagine how the obstacles are overcome. The human chromosome is 3
billion or so base pairs. If one ended up with eight base pair fragments
there would be 4^8 (or almost 17 million) possible sequences; this means
close to 200 positions in the chromosome would have each combination. So one
would apparently need to work with even longer chains. In addition I suspect
that splitting the chromosome into smaller parts would be very unspecific.

In sequencing proteins one works with much smaller molecules with the
additional advantages that there are twenty-two amino acids and one can
create conditions of fairly specific cleaving.

Perhaps the scientific community is perpetrating a hoax; you know, like
staging the moon landing on a Hollywood set.

There were two basic strategies. One was to create large insert
libraries YACs and BACs etc.) where you created a physical map of each
chromosome with overlapping long pieces of DNA 100,000 to several
million base-pairs long, and each long "clone" of DNA was sequenced.
The other was "shot gun" sequencing where the genome was chopped up
into relatively short overlapping pieces of DNA of around a thousand
base-pairs, and each short piece was sequenced and then all the
overlapping sequences were assembled. Not surprisingly what was
eventually adopted was a combination of the two approaches.

The new technologies can sequence hundreds of thousands of short DNA
sequences at the same time and generate a gigabase of DNA sequence in
a single run (look up Solexa or Illumina). Currently the fragments
generated from such technologies are not of optimal length for shotgun
genomic sequencing, but they are adequate for small genomes like
bacterial genomes and they are useful for resequencing genomes that
the new sequence can be compared to. It is part of the push to bring
sequencing of anyones human genome to $1,000.00. They aren't there
yet.

Ron Okimoto

.

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