Personalized Medicine - Translational Informatics: Realizing the Promise of Knowledge-Driven Healthcare - page 35

Genomics, headed up by J. Craig Venter, performed a parallel effort [ 2 ]. This private
effort initially intended to retain their sequence data as proprietary, but later made it
available for non-commercial use [ 3 ]. With the completion of these draft sequences,
which took approximately 10 years and $100 million [ 4 ], scientists had the “parts
list” for human cellular biology. However, in much the same way that a parts list for
a Boeing 747 would not be suffi cient for building an airplane, or troubleshooting it
once it was built, a genomics parts list is only the beginning. The key information is
how all the different parts work together. Upon sequencing the human genome,
then, the focus shifted from cataloging the parts to understanding what each of those
parts does both individually and collectively. This transition helped to bring about a
radical change from the reductionist approach used in the past to a more holistic and
dynamic systems approach used widely in biological research today.
The word “genome” was coined in 1930 as a combination of the words “gene”
and “chromosome.” Despite the term's venerability, the fi eld of genomics arguably
only came into its own in the mid-1990s with the invention of DNA microarrays,
which enabled measurement of gene expression across tens of thousands of genes at
one time. These chips, no bigger than a microscope slide, are printed with specifi c
DNA sequences from known genes. The general approach entails labeling cellular
RNA (i.e. the RNA that is present in cells for genes that are activated or “turned on”)
with fl uorescent dyes and then washing the labeled RNA over the chips. Through
complementary base pairing, the labeled RNA only sticks to spots with a matching
sequence (Fig. 3.3 ). Spots that light up when viewed with a laser scanner indicate

Tissue of
interest

RNA Labeled cDNA

Fluorescent scanner
quantitates spot intensities

Labeled molecules bind to specific sequences on chip

Fig. 3.3 Overview of DNA microarrays. Messenger RNA is extracted from the cells of interest
and serve as a template for the creation of labeled cDNA. Those labeled molecules are then washed
over a chip printed with known, gene-specifi c sequences at known coordinates. A fl uorescent laser
scanner is then used to detect the intensity of each spot, which corresponds to the amount of RNA
that was present in the cell for each of the genes represented on the chip