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Introduction to Genomics

What's a Genome?

Genome is a fancy word for all your DNA. From potatoes to puppies, all living organisms have their own genome. Each genome contains the information needed to build and maintain that organism throughout its life. 

Your genome is the operating manual containing all the instructions that helped you develop from a single cell into the person you are today. It guides your growth, helps your organs to do their jobs, and repairs itself when it becomes damaged. And it’s unique to you. The more you know about your genome and how it works, the more you'll understand your own health and make informed health decisions.

What does my genome look like?

If all the DNA from a single human cell was stretched out end-to-end, it would make a six-foot-long strand comprised of a six billion letter code. It’s hard to imagine how that much DNA can be packed into a cell’s nucleus, which is so small it can only be seen with a specialized microscope. The secret lies in the highly structured and tightly packed nature of the genome.

The DNA Double Helix

Genomes are made of DNA, an extremely large molecule that looks like a long, twisted ladder. This is the iconic DNA double helix that you may have seen in textbooks or advertising.

DNA is read like a code. This code is made up of four types of chemical building blocks, adenine, thymine, cytosine, and guanine, abbreviated with the letters A, T, C, and G. The order of the letters in this code allows DNA to function in different ways. The code changes slightly from person to person to help make you who you are.

DNA bases


The DNA in a cell is not a single long molecule. It is divided into a number of segments of uneven lengths. At certain points in the life cycle of a cell, those segments can be tightly packed bundles known as chromosomes. During one stage, the chromosomes appear to be X-shaped.

Every fungus, plant, and animal has a set number of chromosomes. For example, humans have 46 chromosomes (23 pairs), rice plants have 24 chromosomes, and dogs have 78 chromosomes.

Human chromosomes


How does my genome work?

An instruction manual isn’t worth much until someone reads it. The same goes for your genome. The letters of your genome combine in different ways to spell out specific instructions.


A gene is a segment of DNA that provides the cell with instructions for making a specific protein, which then carries out a particular function in your body. Nearly all humans have the same genes arranged in roughly the same order and more than 99.9% of your DNA sequence is identical to any other human.

Still, we are different. On average, a human gene will have 1-3 letters that differ from person to person. These differences are enough to change the shape and function of a protein, how much protein is made, when it's made, or where it's made. They affect the color of your eyes, hair, and skin. More importantly, variations in your genome also influence your risk of developing diseases and your responses to medications.

  • people
  • Rice 41,000 genes
  • bread mold
  • Streptococcus group A - strep throat
  • Chicken pox virus
Your Genome

The Role of Your Parents

The instructions necessary for you to grow throughout your lifetime are passed down from your mother and father. Half of your genome comes from your biological mother and half from your biological father, making you related to each, but identical to neither. Your biological parents' genes influence traits like height, eye color, and disease risk that make you a unique person.

Your Life Your Environment

Does my genome determine everything about me?

Not entirely. Genomes are complicated, and while a small number of your traits are mainly controlled by one gene, most traits are influenced by multiple genes. On top of that, lifestyle and environmental factors play a critical role in your development and health. The day-to-day and long-term choices you make, such as what you eat, if you smoke, how active you are, and if you get enough sleep, all affect your health.

DNA is not your destiny. The way you live influences how your genome works.

What causes genetic diseases?

A genetic disease is caused by a change in the DNA sequence. Some diseases are caused by mutations that are inherited from the parents and are present in an individual at birth. Other diseases are caused by acquired mutations in a gene or group of genes that occur during a person's life.

Genetic Variants

Changes in the DNA sequence are called genetic variants. The majority of the time genetic variants have no effect at all. But, sometimes, the effect is harmful: just one letter missing or changed may result in a damaged protein, extra protein, or no protein at all, with serious consequences for our health. Additionally, the passing of genetic variants from one generation to the next helps to explain why many diseases run in families, such as in sickle cell disease, cystic fibrosis, and Tay-Sachs disease. If a certain disease runs in your family, doctors say you have a family health history for that condition.

​Genetic Disorders | NHGRI
Genetic Disorders

A list of genetic, orphan and rare diseases under investigation by researchers at or associated with the National Human Genome Research Institute.

About Autism | NHGRI
About Autism

Autism is characterized by impaired social interactions, problems with verbal and nonverbal communication and repetitive behaviors.

About Breast Cancer | NHGRI
About Breast Cancer

Breast cancer is the second most common cancer in women after skin cancer.

About Cystic Fibrosis | NHGRI
About Cystic Fibrosis

Cystic fibrosis is a genetic disease that causes the body to produce thick, sticky mucus that clogs the lungs, leads to infection, and blocks the pancreas.

About Down Syndrome | NHGRI
About Down Syndrome

Down syndrome is a chromosomal condition related to chromosome 21.

​About Parkinson's Disease | NHGRI
About Parkinson's Disease

Parkinson's disease is a neurological condition that typically causes tremor and/or stiffness in movement

​Sickle Cell Disease | NHGRI
About Sickle Cell Disease

Sickle cell disease is a group of inherited red blood cells disorders.

About Wilson Disease | NHGRI
About Wilson Disease

Wilson disease is a rare genetic condition that causes a person's body to store too much of the mineral copper, leading to organ damage that may cause death.

Attention Deficit Hyperactivity Disorder (ADHD) | NHGRI
About Attention Deficit Hyperactivity Disorder

Attention Deficit Hyperactivity Disorder (ADHD) is a neurological disorder that affects a person's ability to control their behavior and pay attention to tasks.

What is genetic testing?

Genetic testing consists of the processes and techniques used to determine details about your DNA. Depending on the test, it may reveal some information about your ancestry and the health of you and your family.

Predictive testing is for those who have a family member with a genetic disorder. The results help to determine a person’s risk of developing the specific disorder being tested for. These tests are done before any symptoms present themselves. 

Diagnostic testing is used to confirm or rule out a suspected genetic disorder. The results of a diagnostic test may help you make choices about how to treat or manage your health.

Pharmacogenomic testing tells you about how you will react to certain medications. It can help inform your healthcare provider about how to best treat your condition and avoid side effects.

Reproductive testing is related to starting or growing your family. It includes tests for the biological father and mother to see what genetic variants they carry. The tests can help parents and healthcare providers make decisions before, during, and after pregnancy.

Direct-to-consumer testing can be completed at home without a healthcare provider by collecting a DNA sample (e.g., spitting saliva into a tube) and sending it to a company. The company can analyze your DNA and give information about your ancestry, kinship, lifestyle factors and potential disease risk.

Forensic testing is carried out for legal purposes and can be used to identify biological family members, suspects, and victims of crimes and disasters.

What are the benefits for my health?

One way genomics research can benefit you is through the emerging field of precision medicine. Specifically, characteristics of your genome can help predict how you will react to certain medications, allowing your healthcare provider to choose the appropriate prevention or treatment options for you.

Pill box

How does genomics impact everyday life?

As technology advances and we learn more about how the genome works, information about our genomes is quickly becoming part of our everyday life. Emerging technologies give us the ability to read someone’s genome sequence. Having this information can lead to more questions about what genomics means for ourselves, our family members and society.

Impact on Society

Whether you realize it or not, many parts of our daily lives are influenced by genomic information and technologies. Genomics now provides a powerful lens for use in various areas, including medical decisions, food safety, ancestry and more. 

Last updated: October 11, 2019