318
GENES CAN MOVE
FROM SPECIES
TO SPECIES
MICHAEL SYVANEN (1943–)
T
he continuity of life—the
growth, reproduction, and
evolution of organisms—is
widely seen as a vertical process,
driven by genes passed down from
parents to offspring. But in 1985,
American microbiologist Michael
Syvanen proposed that, rather than
being simply passed down, genes
could also be passed horizontally
between species, independently
of reproduction, and that horizontal
gene transfer (HGT) plays a key
role in evolution.IN CONTEXT
BRANCH
BiologyBEFORE
1928 Frederick Griffith shows
that one strain of bacteria can
be transformed into another,
by the transfer of what is later
found to be DNA.1946 Joshua Lederberg and
Edward Tatum discover the
natural exchange of genetic
material in bacteria.1959 Tomoichiro Akiba and
Kunitaro Ochia report that
antibiotic-resistant plasmids
(rings of DNA) can move
between bacteria.AFTER
1993 American geneticist
Margaret Kidwell identifies
instances where genes have
crossed species boundaries
in complex organisms.2008 American biologist
John K. Pace and others
present evidence of horizontal
gene transfer in vertebrates.Back in 1928, British physician
Frederick Griffith was studying the
bacteria implicated in pneumonia.
He found that a harmless strain
could be made dangerous simply
by mixing its living cells with the
dead remnants of a heat-killed
virulent one. He attributed his
results to a transforming “chemical
principle” that had leaked from the
dead cells into the living ones. A
quarter of a century before DNA’s
structure was unlocked by James
Watson and Francis Crick, GriffithHeat-killed bacteria
can transfer their
characteristics
to living bacteria.Similar genes
have been identified
in distantly related
species of organisms,
including vertebrates.This happens because
genes can move between
bacterial cells.Genes can
move from species
to species.