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Genetic Testing Guide
Learn The Basics
InteliHealth Medical Content


Reviewed by the Faculty of Harvard Medical School


Amino acids — Twenty chemical "building blocks" that link together to form proteins. All amino acids have the same backbone, but each has a unique "side chain" coming off the backbone that gives it distinct properties. (Picture charms on a charm bracelet.)

BRCA1/BRCA2 — Genes that have been linked to breast and ovarian cancers. Proteins built by these genes help the cell repair damaged DNA. When the BRCA1 or BRCA2 proteins don't work properly, cells can multiply out of control, leading to cancer.

Cancer — A disease in which cells in the body multiply out of control. These cells can spread to other organs in the body.

Carrier — A person who has one mutated copy of a recessive gene and one unchanged or normal copy of the same gene. For genes on the X chromosome, a woman can also be a carrier of one abnormal gene because women have two X chromosomes. Typically, carriers do not show any symptoms from carrying the mutated gene, but they can pass it on to their children.

Cell — The basic unit of a living organism. The cell contains the organism's genome, as well as the materials to build proteins. Cells can have specialized roles within the body. For example, nerve cells tell muscle cells to contract or relax.

Chromosome — The “packaged” form of DNA found in most of the body's cells. Humans have 46 chromosomes: 23 are inherited from the father and 23 from the mother.

An illustration showing that DNA lives within chromosmes, which live within cells.
Where does DNA live?
The long fibers of your DNA are wound up tightly into X-shaped chromosomes for easier storage within the nucleus of your cells.

Codon — A grouping of three nucleotide bases within a gene that represents one amino acid or gives the cell directions to start or stop construction of a protein. For example, the codon "CAA" tells the cell to add the amino acid glutamine to the protein being made. The codon "TAA" tells the cell to stop making a protein.

Complex Genetic Diseases — Complex diseases are influenced by many genes, and even by changes in the DNA outside of a gene. One of these genetic changes acting alone would not cause a disease, but many changes acting together could cause disease. Examples of complex genetic diseases include asthma, diabetes and heart disease.

DNA — The abbreviation for deoxyribonucleic acid, the genetic material we inherit from our parents. It is found in nearly all cells in the body.

An illustration of a DNA double helix
What is DNA?
DNA is the chemical material you inherited from your parents. It makes you different from every person who has ever existed (unless you're an identical twin).

DNA microarrays — A technology that uses DNA to learn how large numbers of genes, and the proteins they make, work together in cells. Microarrays are one tool for figuring out a cancer tumor's signal, for example. If the signal can be identified, it may be possible to create a drug or antibody to "intercept" the message, preventing or "turning off" the cancer.

Dominant genes — If a disease is inherited through a mutation in a dominant gene, only one copy of a mutation is needed in order to see the effects. The mutated gene dominates over the normal, unchanged copy of the same gene.

Genes — Areas of DNA found on every chromosome that "tell" the cell how to build proteins.

Gene therapy — A treatment for diseases that substitutes normal pieces of DNA for abnormal so that normal proteins can be made. This is still in the research phase.

Genetic tests — Laboratory tests that examine DNA, chromosomes, or proteins to look for genetic mutations that cause diseases.

Genome — All of the DNA found in an organism's chromosomes.

Human Genome Project — An international effort to map the entire human genome. This was completed in 2003.

International HapMap Project — An international effort to catalog the differences at SNPs (see below) among several populations including Africans, Caucasians, Chinese and Japanese. Differences at SNPs partially explain why some people are more susceptible to common diseases like age-related macular degeneration, diabetes, heart disease and rheumatoid arthritis. This was completed in 2006.

Mutation — A change in the DNA sequence. Mutations can be inherited or they can occur spontaneously. If DNA in an egg or sperm contains a mutation, the mutation may be passed on to the next generation.

Nucleotide bases — The building blocks of DNA. There are four nucleotide bases: adenine (A), thymine (T), guanine (G) and cytosine (C).

An illustration showing DNA with four bases: T, C, A, G.

Protein — Molecules that are responsible for thousands of processes, structures, and materials in your body. Proteins consist of one or more chains of amino acids.

Recessive gene — If a disease is caused by a mutation in a recessive gene, two copies of a mutated gene are required before the effects will occur in the body.

RNA — Abbreviation for ribonucleic acid. RNA uses the DNA code to help to build proteins. The structure of RNA is similar to that of DNA.

Single-gene diseases — Diseases that result from one or more mutations in only one gene. Examples include cystic fibrosis and Tay-Sachs disease.

SNPs — Abbreviation for single nucleotide polymorphisms. SNPs are changes in one nucleotide in the DNA sequence (for example, A to G, or G to T) that occur in at least 1 percent of a large population. Humans have about 10 million SNPs. SNP patterns may be different between a group of people with a disease versus a group of healthy people. These comparisons help scientists understand the cause of complex genetic diseases. SNPs can also be used to follow inheritance patterns in families.

Illustrations By InteliHealth Designer Lisa Ormerod 




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Last updated June 10, 2014

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