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Studying Genes

What are genes?

Shiny DNA helix.

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 the next.

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 genes.

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 read.

Is genetic variation related to health and disease?

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 risk.

Genetic test.

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 population groups?

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 permission?

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 organisms?

Another DNA chip.

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.

Learn more:
The New Genetics

NIGMS is a part of the National Institutes of Health that supports basic research to increase our understanding of life 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

Content revised November 2012

This page last reviewed on December 11, 2012