What are genes?
Genes are sections of DNA that contain instructions for making
the molecules—many of which are proteins—that perform
the body's functions. Genes are passed from one generation to
What is a genome?
A genome is all of the genetic material in an organism. This
includes genes and DNA elements that control the activity of
Does everybody have the same genome?
While the human genome is mostly the same in all people, there
are slight differences. This genetic variation, spread across the
genome, makes up about one-tenth of a percent of each person's DNA.
These small differences are enough to create people with different
appearances and different health. However, the more closely related
two people are, the more similar their DNA is likely to be.
Another type of genetic variation, called epigenetic, does not
involve differences in DNA itself. Rather, it arises from chemical
tags that attach to DNA and affect how its instructions are
Is genetic variation related to health and
Many differences in DNA have no effect on health or disease
risk, but some do. Because parents pass their genes on to
offspring, some diseases tend to cluster in families, similar to
other inherited traits. However, many factors other than genes,
including diet, exercise and environmental exposure, also
contribute to health and disease.
Genetic variations can influence how people respond to certain
medicines, as well.
What does it mean to have a genetic risk?
Having a genetic risk means that a person has inherited the
tendency to develop a certain illness. It does not mean that he or
she will definitely develop the illness, but rather that there is a
higher chance of developing it than if he or she did not have the
What can a genetic test reveal?
This type of test can identify genetic changes that have been
linked to the risk of developing a specific disease or of passing a
disease gene on to descendants. A genetic test can also indicate
how a person might respond to certain medicines.
Why does genetic research sometimes involve specific
Members of population groups have mostly similar genomes, which
makes it easier for scientists to spot rare differences that could
be related to health or disease. In addition, some medical
conditions are more common in certain population groups, and
populations may share diets, environments and other characteristics
that influence health.
Can researchers study someone's genes without
Scientists who conduct research with people are required to
follow strict rules that include obtaining signed consent from
participants. Before collecting DNA samples, researchers must tell
participants the purpose of the study, how the samples will be
used, and whether and for how long the samples will be stored.
Why do scientists study the genes of other
Because all living things evolved from a common ancestor,
humans, animals and other organisms share many of the same genes.
For example, the human and chimpanzee genomes are 96 percent
identical, and the human and mouse genomes are about 85 percent the
same. By comparing the genomes of different species, particularly
genes that have been preserved in multiple organisms over millions
of years and the elements that control the activity of those genes,
scientists can find similarities and differences that improve their
understanding of how human genes function and are regulated. This
helps researchers develop new strategies to treat and prevent human
disease. Scientists also study the genes of bacteria, viruses and
fungi to find ways to prevent or treat infection and, increasingly,
to learn how the microbes on and in the body affect human health,
sometimes in beneficial ways.
NIGMS is a part of the National Institutes of Health that
supports basic research to increase our understanding of biological
processes and lay the foundation for advances in disease diagnosis,
treatment and prevention. For more information on the Institute's
research and training programs, visit http://www.nigms.nih.gov.
Content revised November 2012