Genetics FAQ

This page will provide you with some background information to help you understand your genetic diagnosis.


What is a GENOME?

A genome is what we call ALL the genetic material in our body’s cells. Inside our genome we have a set of instructions (genes), half we get from our mother and half from our father.

Our genome is made up of four “letters” of deoxyribonucleic acid (DNA): A, T, C, and G. These letters make up the instructions that our body uses to function.


WHERE is our genome?

The human body is made up of tiny cells. Cells are the building blocks of our body. They make up our skin, bones, blood and more.

Each of our cells, with a few exceptions, has a copy of all of our genetic information. The strands of DNA are tightly wound into structures called chromosomes.


What are GENEs?

Each cell in the human body contains more than 20,000 genes. Genes carry the information that determines what you look like and how your body grows and develops. Genes are made up of the four letters of DNA: A, T, C, and G. Different combinations of these letters make up each of our genes.

You, like every other person, have two sets of chromosomes, 23 from your mother and 23 from your father, for a total of 46. This also means that you have two copies of each gene.

Chromosomes numbered 1-22 are the same in both males and females. The last pair, the 23rd pair, determines a person’s sex. A person who has XX, or two X chromosomes, will be a female (shown above). A person who has XY, or one X chromosome and one Y chromosome, will be a male (not shown).



genetic change is also sometimes called a gene change, mutation, variant, or difference.

Each of us contain differences in our genomes that make us unique. Most of these differences have little or no impact on our health. But some do.

Some genetic differences are large in size, such as an extra chromosome.  For example, an extra chromosome 21 results in a condition called Down syndrome.

A person with this set of chromosomes would have Down syndrome.
There can also be extra or missing parts of a chromosome (duplications or deletions). For example, a 16p11.2 duplication/deletion is associated with autism. Duplications and deletions are also called copy number variants (CNVs).

A person missing the 16p11.2 part of their 16th chromosome would have a 16p11.2 deletion, which is associated with autism.

Sometimes when a DNA letter is missing or altered in a gene, it can prevent cells from functioning correctly. For example, alterations in a specific gene on chromosome 7 can lead to a condition called cystic fibrosis.


What do genes DO?

Each gene is a set of instructions to make proteins that allow the body to grow, fight infection, turn food into energy, and do everything else the body does. Most people will have two copies of each gene, one from their mother and one from their father.

Some genes give instructions for our physical features, like our hair color, blood type, height, and skin color. Other genes are important for development of the body before a baby is born, brain function, or the person’s ability to heal from a wound.

If a person has a genetic change in a gene that’s important for health and development and that gene does not work properly, the person may have symptoms of a genetic condition.


Is my genome UNIQUE?

People come in many shapes and sizes, but in general we are all very similar at the DNA level. The DNA of any two people is 99.9% the same.

Still, the small amount of DNA that is different among people is very important. DNA differences are part of what makes each of us unique. They affect the color of your eyes, hair, and skin. They can also influence your risk of certain conditions and your response to drugs.


So is everything determined by my DNA?

No. Your DNA is just one part of who you are. When it comes to your health, also important are lifestyle and environmental factors such as the food you eat, the quality of the air you breathe, how much sleep you get, and how much exercise you get.


Are all genetic differences BAD?

No. Most genetic variants do not affect how your body functions.

There are several different types of genetic differences:

  • Normal variations are differences in a gene that are not known to cause health, developmental, or behavior problems. For example, different blood types result from normal genetic variations found in humans.
  • Disease-causing(pathogenic) variations are differences in genes that cause a specific condition or disorder. For example, changes in a gene on chromosome 7 lead to a person having cystic fibrosis.
  • Disease-risk variations are differences in genes that affect a person’s risk of developing a specific condition or disorder. For example, some genetic variations in cancer genes can increase a person’s risk of developing cancer, but they do not mean the person will definitely get cancer.
  • Unknown or new variations are differences whose effects are unknown. There are thousands of letters in a gene, and the scientific community does not know what all possible changes mean. Whether some changes contribute to a developmental difference or are normal variations has yet to be learned.

How are genetic differences inherited or passed down?

A genetic duplication or deletion or a difference in one gene can be passed down from parent to child. However, gene changes are not always inherited. Sometimes, the gene change is present for the first time in a child. This is called a de novo change.

Below is an example of a gene change that is not inherited.

A spontaneous gene change in an egg or sperm cell can result in a genetic condition in one child in a family — a de novo change.


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