pacificstandard | Today, DNA is central to modern biology, but scarcely a century ago
biologists were debating whether or not genes actually existed. In his
1909 textbook on heredity, Danish botanist Wilhelm Johannsen coined the term gene
to refer to that hereditary “something” that influences the traits of
an organism, but without making a commitment to any hypothesis about
what that “something” was. Just over a decade later, a prominent
biologist could still note that some people viewed genes as “a convenient fiction or algebraic symbolism.”
As the century progressed, biologists came to see genes as real
physical objects. They discovered that genes have a definite size, that
they are linearly arrayed on chromosomes, that individual genes are
responsible for specific chemical events in the cell, and that they are
made of DNA and written in the language of the Genetic Code.
By the time the Human Genome Project was initiated in 1988, researchers
knew that a gene was a segment of DNA with a clear beginning and end
and that it acted by directing the production of a particular enzyme or
other molecule that did a specific job in the cell. As real things,
genes are countable, and in 1999 biologists estimated that humans had “80,000 or so” of them.
Yet, when the dust from the Human Genome Project cleared, we didn’t have nearly as many genes as we thought. By the latest count,
we have 20,805 conventional genes that encode enzymes and other
proteins. Our inflated gene count, though, wasn’t the only casualty of
the Human Genome Project. The very idea of a gene as a well-defined
segment of DNA with a clear functional role has also taken a hit, and as
a result, our understanding of our relationship with our genes is
changing.
One major challenge to the concept of a gene is the growing evidence
that many genes are shapeshifters. Instead of a well-defined segment of
DNA that encodes a single protein with a clear function, we should view a
gene as “a polyfunctional entity that assumes different forms under
different cellular states,” according to University of Washington biologist John Stamatoyannopoulos. While researchers have long known
that genes are made up of discrete subunits called “exons,” they hadn’t
realized until recently the degree to which exons are assembled—like
Legos—into sometimes thousands of different combinations. With new
technologies, biologists are cataloging these various combinations, but
in most cases they don’t know whether those combinations all serve the
same function, different functions, or no function at all.
