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One of the tediously
repetitive tasks of molecular genetics is
transferring randomly plated bacterial colonies,
as seen in the foreground video image, to
microtitre array plates. An automated colony
picker robot developed at Berkeley, then modified
at Livermore, can pick 1000 colonies per hour and
place them in array plates such as the one being
examined here by a Livermore researcher. |
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| Photolithographic techniques
inspired by the semiconductor industry are the
basis for preparing high-density oligonucleotide
arrays. Shown here is a 1.28x1.28Ðcm array of
more than 10,000 different nucleotide sequences
(probes), which was then incubated with a cloned
fragment (the target) from the genome of the
HIV-1 virus. If the fluorescently labeled target
contained a region complementary to a sequence in
the array, the target hybridized with the probe,
the extent of the hybridization depending on the
extent of the match. This false-color image
depicts different levels of detected fluorescence
from the bound target fragments. Techniques such
as this may ultimately be used in sequencing
applications, as well as in exploring genetic
diversity, probing for mutations, and detecting
specific pathogens. Photo courtesy of Affymetrix. |
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Sequencing based on the
detection of fluorescence from single molecules
is being pursued at Los Alamos. The strand of DNA
to be sequenced is replicated using nucleotides
linked to a fluorescent tag -- a different tag
for each of the four nucleotides. The tagged
strand is then attached to a polystyrene bead
suspended in a flowing stream of water, and the
nucleotides are enzymatically detached, one at a
time. Laser-excited fluorescence then yields the
nucleotide sequence, base by base. Much
development remains to be done on this technique,
but success promises a cheaper, faster approach
to sequencing, one that might be applicable to
intact cosmid clones 40,000 bases long. |
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