Number 171, April 1, 1994 by Phillip F. Schewe and Ben Stein
FASTER TECHNIQUES FOR SEQUENCING DNA , described at the American Physical
Society (APS) March Meeting in Pittsburgh, may contribute to the Human
Genome Project. With the conventional technique, known as gel electrophoresis,
in which DNA fragments are separated by electric fields, it would take
20,000 man-years to determine the complete sequence of 3 billion "base
pairs" that make up the human genetic code. In a modification of electrophoresis
that uses thinner gels and higher electric fields, Lloyd Smith of the University
of Wisconsin can now sequence a 500 base-pair DNA fragment in an hour,
as opposed to the 12-14 hours it takes normally. Brian Chait of Rockefeller
University has devised a sequencing method that completely bypasses the
use of a gel. In his method, a laser pulse would zap DNA fragments, converting
them into gaseous ions which would then fly towards a detector to be analyzed.
Once his technique is refined, Chait estimates that an amount of DNA code
that normally takes several hours to sequence could be analyzed in less
than a minute. Other researchers in Pittsburgh proposed sequencing methods
based on photolithography techniques and single-molecule detection.
PUNCTUATED EQUILIBRIUM is the name for Harvard paleontologist Stephen
Jay Gould's theory that evolution comes about not just by gradual steps
but sometimes because of catastrophic events, such as meteor impacts. Kim
Sneppen of the Niels Bohr Institute in Denmark, speaking at the APS meeting,
believes that evolutionary bursts may also occur because of the dynamics
of ecological systems themselves. Sneppen and his colleague Per Bak of
Brookhaven have proposed a model in which biological species can exhibit
"self-organized criticality," according to which some systems,
such as sand dunes or geological faults, can accommodate the gradual addition
of energy or stress or small increments of matter until a certain threshold
is crossed, after which a catastrophic reordering takes place, such as
an earthquake or avalanche. Sneppin's model, employing various rates of
mutation and interactions among species, seems to forecast such avalanches
for biological systems. (Science News, 26 March 1994.)
WOMEN IN PHYSICS account for only 15% of bachelor's degree recipients,
11% of new PhD's, and only 3% of tenured or tenure-track positions in the
U.S. This compares poorly with the comparable numbers for many other nations
with advanced physics establishments. For example, recent women physics
PhD percentages were 18% in Germany, 21% in France, 12% in Britain, and
25% in the former Soviet Union. In the other direction, the number for
Japan was only 4%. (Science, 11 March 1994.)
NEUTRINO OSCILLATIONS , the transformation of one neutrino type (electron,
muon, or tau) to another, is invoked to explain the solar neutrino problem:
a detector designed to monitor electron-type neutrinos from the sun will
fail in its job if, on the way to Earth, electron neutrinos are turning
into muon neutrinos. A new generation of terrestrial experiments searching
for neutrino oscillation are now being planned. All involve accelerator-produced
neutrinos and the study of their fluxes at various points along a baseline.
One scheme uses neutrinos from CERN in Switzerland and a detector at Gran
Sasso in Italy, 732 km away. Another experiment involves shooting neutrinos
from Fermilab, near Chicago, up to the Soudan II detector in Minnesota.
(Science, 18 Feb.)
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