How Was It Discovered? 221
At that time, scientists believed that human DNA contained about 100,000 genes
spread along 23 chromosomes locked onto DNA’s double helix, held together by over 3 billion base pairs of molecules. Watson’s task was to identify, interpret, and sequence every
gene on every chromosome, as well as every one of those billions of base pairs.
Certainly, the ability to identify and sequence individual pairs existed. Watson’s problem was one of size. Using the existing (1990) technology, it would take thousands of years
for all existing labs to complete the identification and sequencing of three billion pairs.
Watson decided to start with large-scale maps of what was known about chromosomes
and work down toward the details of individual pairs. He directed all IHGSC scientists to
work toward creating physical and linking maps of the 23 chromosomes. These maps would
provide an overview of the human genome and would include only those few “snippets” of
actual gene sequences that were already known.
By 1994 this first effort was complete. Watson ordered IHGSC scientists to map the
complete genome of the simplest and best-known life forms on Earth to refine their technique before attempting to work on the human genome. IHGSC scientists chose fruit flies
(studied extensively since 1910), e. coli (the common intestinal bacterium), bread molds,
and simple nematodes (tiny oceanic worms). In the mid-1990s, work began on mapping the
tens of millions of base pairs in these simple genomes.
However, not all biologists agreed with this approach. J. Craig Venter (a gene sequencer at the Institutes of Health) believed that scientists would waste precious years focusing on Watson’s “big picture” and should instead sequence as many specific parts of the
genome as they could and piece these individual sequences together later.
A war began between Watson (representing the “top down” approach) and Venter
(representing the “bottom up” approach). Accusations and ugly words erupted from both
sides at congressional hearings, at funding meetings, and in the press.
Venter quit his government position and formed his own company to develop as much
of the genome sequence as he could ahead of IHGSC’s effort. In 1998 Venter shocked the
world by announcing that he would use linked supercomputers to complete his sequencing
of the entire human genome by 2002, three years ahead of IHGSC’s timetable.
In early 2000 President Clinton stepped in to end the war and merged both sides into a
unified genome effort. In 2003 this merged team released their preliminary report, detailing
the entire sequence of the human genome. In written form, that genome would fill 150,000
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