1994, it was the germ that causes the flu. In 2000, it was human
beings. Then mice, rice, and, in 2004, dogs. Call it a map, a
diagram, a pattern, a problem, a miracle: it's genomics.
is the study of all the genes in a living organism and what they
do. When you have the genome of an organism, you have a complete
catalog of everything that organism is capable of doing -- how
it functions, the nutrients it needs to grow, and how it senses its environment.
Extreme 2004 researchers want to know how the Pompeii worm survives
the hot, toxic environment at hydrothermal vents. For clues, they
will be searching through the genome of the bacteria that live
right on the worm's back!
you set out on your voyage into genomics, let's start with some
basic concepts and terms behind this growing scientific field. We'll talk about them in the context of a very important subject -- you!
Your genome is
your life's "instruction book," passed
down to you from your parents.
You inherited all this
genetic information from them and the generations before them.
Coded into your personal wiring diagram is all kinds of information,
from the color of your eyes, to your height, to whether or not
you like pizza, and much more. Every single cell in
your body contains your genome.
is made up of chromosomes, which contain genes, which contain
a Genome?, an
excellent on-line resource presented by the Genome
News Network, describes these
relationships as a set of Chinese boxes nested inside each other.
Let's take a closer look.
A chromosome is a package of hereditary information
in each of your cells. Since a chromosome contains some of your genes,
it's part of your genome. In most organisms, chromosomes look like
bits of yarn and live in the nucleus of a cell. Every chromosome
contains a single, long molecule of DNA surrounded by proteins that
keep it folded into an orderly shape. If you could stretch out this
long, skinny strand of DNA, it would reach over 3 inches.
few simple bacteria have only one chromosome, which contains the
organism's entire genome. In most organisms, however, genetic information
is divided up among a number of different chromosomes. As you can
see on the chart at left, we humans have 46 chromosomes, a sunflower
has 34, and a dog has 78. Organisms with a similar number of chromosomes
tend to be closely related. For example, humans have 46 chromosomes
in each of their cells, and chimpanzees have 48. And we're not
important fact about chromosomes is that they come in pairs. Every
healthy human cell contains 23 pairs of chromosomes. You received
one member of each pair from your mother and one from your father.
In humans, one pair of chromosomes determines your sex, with XY
for males, and XX for females.
the chromosomes of any species may look alike, they vary in
size and shape, and each one contains different genes.
contain the information about who you are. They are responsible
for different characteristics, such as the color of your hair
or the shape of your nose or whether you are at high risk
of developing a certain disease.
A single gene can affect several traits, and, vice versa, a
can be affected by several genes. Each of
us has two copies of every human gene, one from
each of our parents. Your characteristics depend on how these
two copies interact.
of your genes carries the instructions for making only one
certain protein. Proteins are
critical to every aspect of your body's function. For example,
insulin is a protein important in regulating your metabolism
-- how you break down food, store it as energy, and then use
the energy to rid your body of wastes. If your pancreas, a
gland behind your stomach, does not produce enough insulin,
a disease called diabetes will develop.
tell your cells which proteins to make, how much, when, and where.
Within a gene, these instructions are divided up into little sections
of DNA called exons that
are interspersed with non-coding "junk" sections
of DNA called introns.
sequences in genes determine which genes get "switched on" or "expressed" to
transmit their protein-making instructions to a cell. Since
all of your cells contain the same genes, it's the genes that
are turned on that make a cell in your heart different from a cell
in your brain.
many genes do humans have? Scientists with the International Human
Genome Sequencing Consortium, led in the United States by the National
Human Genome Research Institute and the Department of Energy, published
their description of the finished human genome sequence on October
21, 2004, reducing the estimated number of protein-coding human
genes from 35,000 to only 20,000-25,000. Some scientists view this
as a surprisingly low number for our species.
stands for deoxyribonucleic acid. It represents all the hereditary
material in living cells. It's the stuff that genes and genomes
are made of. While a gene contains just enough DNA to code for
one protein; the genome represents all the DNA in an organism.
Swiss scientist Friederich Miescher isolated the white, slightly
acidic DNA from cells in 1869. He called it "nuclein." Later,
in 1953, James Watson and Francis Crick discovered that the DNA
molecule took the form of a double helix -- a spiral staircase
or ladder. The sides of the ladder are composed of alternating
molecules of sugar and phosphate, while the "rungs" consist of
linked chemical building blocks, or "bases," including adenine, cytosine, guanine, and thymine. These four
bases, abbreviated A, C, G, and T, are the letters in the genetic
alphabet. Adenine (A) is always paired with thymine (T), and
cytosine (C) is always paired with guanine (G).
human genome contains over 3 billion base pairs of DNA. Other
organisms have even more, like the lily genome, with 100 billion.
Genome sequencers are helping scientists figure out the order that
these letters of the genetic alphabet appear in. Clues in the DNA
sequence, hard work, and luck are helping scientists home in on
genes of particular interest, such as those associated with certain
the tremendous catalog of information that genomics provides about
living organisms, this growing discipline holds both great promise
and serious ethical questions for our future, in areas ranging
from human health, to new methods of food production. What role
has genomics played in your life, and how do you think it will
affect your future?
Genome News Network: What's a Genome
National Human Genome Research Institute, National Institutes
U.S. Department of Energy,
Human Genome Program: Genomics
and Its Impact on Science and Society: A 2003 Primer