Genetics 101


For clarification on Genetic Terminology: Talking Glossary of Genetic Terms by National Human Genome Research Institute

For a comprehensive downloadable guide to Understanding Genetics: Understanding Genetics by Genetic Alliance



ON THIS PAGE:

What are Genes, and what is a Genetic (or Gene) Mutation?

How do genetic mutations occur?

Are genetic mutations always harmful?

What affects a genetic mutation developing into a condition?

How do I find out if I have a genetic mutation?

What is a Hereditary Condition?

I've heard hereditary genetic mutations "skip" a generation. Is that true?


What are Genes, and what is a Genetic (or Gene) Mutation?

Genes are the blueprints for making all the proteins your body needs to grow, develop and work properly. Most genes come in pairs. One gene copy of each pair is inherited from your mother and the other gene copy from your father.

A Genetic Mutation is a change in a gene that prevents it from making its usual (working) protein. Most mutations can be passed along to future copies of the altered cell in your body. A genetic mutation is a change in a gene, it is also called a gene mutation.

Back to Top


How do genetic mutations occur?

Gene mutations occur in two ways:

1. They are inherited from a parent (called hereditary mutations).

2. They are acquired during a person’s lifetime.

Mutations that are passed from parent to child are called hereditary mutations or germline mutations. This type of mutation is present throughout a person’s life in virtually every cell in the body. A BRCA gene mutation is a hereditary mutation.

For More Information on Genes and Genetic Mutations, please visit:

Understanding Gene Testing: What are Genes?
by Access Excellence at the National Health Museum

What are Genes?
by Breast Cancer.org

The Genetic Basics: What are Genes and What do they Do?
by the National Institute of Health

What are Genes?
by 23andMe

The Basics on Genes and Genetic Disorders
by Teens Health

Downloadable Guide to Understanding Genetics
by Genetic Alliance

What is a gene mutation and how do mutations occur?
by National Institute of Health Genetics Home Reference

Back to Top


Are genetic mutations always harmful?

Although humans are genetically 99.9% identical, we all have differences in our genes that make us unique. Most of these differences are not harmful and have little or no impact on our health (for instance, variations in genes that cause different eye colors). In some cases, a gene variation can cause a small increase or decrease in your chance to develop a disease. More rarely, a gene mutation causes a person to have a specific disease (like cystic fibrosis, Tay Sachs disease or sickle cell disease) or to have an increased chance of developing a specific condition (like breast cancer).

Back to Top


What affects a genetic mutation developing into a condition?

The effect of a genetic mutation (whether it is harmful or not, or whether it will be expressed) depends on three things:

1. How the mutation alters a gene’s function

2.How vital that particular gene is to your health

3.Whether the mutation occurs in all your copies of the gene or just half of the copies. In your cells, there are typically two copies of each gene—one from your mother and one from your father. In order for some conditions to develop, both copies of the gene must have the mutation. These conditions are called recessive disorders; sickle cell anemia is an example. In other cases, a mutation in one copy of the gene can lead to the condition. These conditions are called dominant disorders; Huntington disease is an example. Some people with genetic mutations never develop the corresponding condition. All of us inherit some gene mutations from our parents but do not know about them because we have a working copy of the gene from our other parent protecting us from disease. One copy of a gene can be sufficient for normal functioning. When both copies of a gene are not working this can lead to disease.

For more information on Genetic Mutations and Disease, please visit:

Understanding Cancer Series: Gene Mutations and Disease
by the National Cancer Institute

What are Genetic Disorders?
by Genetic Science Learning Center at the University of Utah

Mutations and health
As part of the National Institute of Health Genetics Home Reference Guide

Back to Top


How do I find out if I have a genetic mutation?

The first step is to meet with a genetic counselor, genetic specialist, or other medical professional to review your family medical history. This will help you find out if there is an indication of a genetic condition in your family, your chances for having the condition, and what that means for your health. Very few disease risks can be tested for but disease risks can be accurately estimated based upon family history information. For some conditions genetic testing is available. As part of genetic counseling, you will learn whether genetic testing is available and whether it may offer useful information to you or your relatives.

Most genetic testing involves having a blood sample drawn and results take a few weeks. Usually, genetic testing is most helpful when a relative with a known genetic condition has testing first in order to figure out if a genetic change (mutation) can be found in the family.

For More information on Genetic Counseling and Genetic Testing, please visit:

What is Genetic Testing?
As part of the National Institute of Health Genetics Home Reference Guide

Genetic Testing for BRCA1 and BRCA2
by the National Cancer Institute

Find a Genetic Counselor in your Area
by the National Society for Genetic Counselors

Back to Top


What is a hereditary condition?

A hereditary condition is one that is caused by one or two copies of a gene mutation. If you have a mutation in a dominantly inherited gene, each time you have a child there is a 1 in 2 chance that your child will inherit the gene mutation and a 1 in 2 chance that your child will inherit the working copy of the gene. If you have a mutation in a recessively inherited gene then you will be unaffected but you can pass the mutation on to your child. A child would be affected with a recessive condition only if s/he inherited a mutation in the same gene from her/his other parent.

For more information on Hereditary Conditions and Mutations, please visit:

What is Hereditary Cancer?
by FORCE

Understanding the Difference Between "Congenital" and "Hereditary" Conditions
by Associated Content

Slide show: How genetic disorders are inherited
by Ohio Health

Inheriting genetic conditions: inheritance patterns and understanding risk
As part of the National Institute of Health Genetics Home Reference Guide

Understanding Cancer Series: Hereditary Mutations
by the National Cancer Institute

Back to Top


I've heard certain hereditary genetic mutations "skip" a generation. Is that true?

Although having a genetic mutation increases the chance of developing its corresponding condition, some people with a mutation never get the disease. Therefore, sometimes it looks like the mutation has “skipped” a generation when you look at a family history. For example, you and your father’s mother both have the same hereditary disease and tested positive for the same genetic mutation, but your father does not have the condition. The genetic mutation did NOT skip generations in this example (your father DOES HAVE this mutation). It’s just that the genetic mutation did not result in your father developing the corresponding condition.

Back to Top

Join the Discussion

Visit our forums to share your opinions about the film or to discuss how BRCA and genetic testing have touched your life of the life of someone you know.

Active forum topics