Glossary

Base

A base, or nucleotide, is the primary structure making up a DNA molecule. There are four different types of bases; each represented by one of four letters (A, C, G, T). These are the letters that make the words of your genetic story. The human genome is estimated to contain about three billion base pairs.

Chromosome

DNA is organized into structures known as chromosomes. These are analogous to the chapters in your genetic book. The human genome is comprised of 23 pairs of chromosomes.

Copy Number Variation

Sometimes several copies of a gene are present in the DNA. When the number of copies is different for one individual compared to another, this is known as copy number variation.

Deletion

A change in the DNA sequence that results from the removal of one or more DNA bases.

Dominant Genotype

A genotype that will appear as a trait or characteristic even if only one copy of the gene appears in the genome.

DNA

DNA stands for deoxyribonucleic acid. Taken all together, your DNA is the story of you.

Duplication

A change in the DNA sequence that results from one or more bases being copied.

Gene

A gene is a DNA segment that carries genetic information. Think of genes as the most important words or sentences in your book. The human genome contains 20,000–25,000 distinct genes.

Genetic counselor

A genetic counselor specializes in communicating genetic information to patients and families. They often work closely with medical geneticists or doctors and convey results from any recommended tests. A genetic counselor is trained in counseling individuals and families who have genetic disorders or heightened risk for a variety of inherited conditions. Specifically, they can help support you and your doctor when making decisions about your health. You can locate a genetic counselor through the National Society of Genetic Counseling.

Genetic disorder

A disease due to a particular genetic sequence that is passed from parent to child. Also known as an inherited disease.

Genetic sequence

A genetic sequence, or DNA sequence, is a chain of bases (represented by letters) that constitutes the primary structure of a DNA molecule and carries information. Your body uses these as master instructions to build and run your body.

Genetic variation

Difference in one individual’s DNA sequence from another. These are, in effect, what makes you uniquely you.

Genome

The full set of hereditary information coded in DNA. This includes genes and a lot more, such as segments of DNA that switch genes on and off. Your genome is what tells your story.

Genotype

In personal genomics, the word genotype often describes a particular DNA sequence in your genome. Your genotype leads to a particular characteristic or trait. This is the word choice in your story.

GINA (Genetic Information Nondiscrimination Act)—U.S. only

On May 21, 2008 the United States Congress passed GINA (Genetic Information Nondiscrimination Act). This act safeguards you from improper use of your genetic information by health insurance companies and employers. For example, GINA generally prohibits group health plans and health insurers from denying healthcare coverage to a healthy individual or charging higher premiums based solely on a genetic predisposition to developing a disease in the future. The legislation also prohibits employers from using an individual's genetic information when making decisions about employment, including hiring, termination, job placement, or promotion.

Individual Genome Sequencing (IGS)

IGS is Illumina’s personal genome sequencing service. It provides a way for people to obtain the sequence of their DNA for personal use. Illumina Clinical Services Laboratory is proud to be the first CLIA-certified, CAP-accredited laboratory to offer IGS. IGS has been developed using the highest standards by a team of licensed professionals, an external ethics advisory board, and experts from a variety of areas. We provide very high quality sequence data (accuracy >99.7%) for more than 90% of the human reference genome. The comprehensive nature of this testing represents a new step in the practice of medicine, in which the results will continue to be meaningful and relevant throughout a person’s lifetime.

Inherited disease

A disease due to a particular genetic sequence that is passed from parent to child. Also known as a genetic disorder.

Insertion

A change in the DNA sequence that results from the addition of one or more bases.

Medical Geneticist

A clinical or medical geneticist is typically a doctor who evaluates patients in the office or at a hospital. This consultation includes a medical history, family history, and a detailed physical examination. The geneticist will review objective data, such as imaging and test information, with you, establish a differential diagnosis, and recommend appropriate diagnostic tests. You can locate a medical geneticist through the American Board of Medical Genetics.

Nucleotide

See base.

Personal Genome Sequencing Services

Personal genome sequencing services provide you with an analysis of your genome using DNA sequencing, allowing you to read most of the three billion letters in your genome, their order, and any changes. It can offer information about your disease risk, carrier status, and insights on your ancestry. Information from a personal genome sequence can be reanalyzed as new discoveries are made.

Personal Genotyping Services

Personal genotyping services provide an analysis of some parts of your genome by looking at a subset of defined locations representing known variations in the genome. It can provide information about your disease risk, carrier status, and insights on your ancestry. They scan pre-defined locations in the genome for a “snapshot” look that is based on the most current discoveries at that time. As new discoveries are made, new genotyping services using the new information need to be performed.

Phenotype

A phenotype is the physical or behavioral characteristic or trait that arises from the information in a genome. This is what your story is telling you.

Recessive genotype

A genotype that requires both copies of a gene to be expressed in the physical characteristic or behavior.

SNP

SNP stands for single nucleotide polymorphism. It is a site in the genome where one letter is often substituted for another. Going back to our story analogy, a SNP can lead to a word change, making your story completely unique.

Substitution

A change in the DNA sequence that results from the substitution of one base for another.

Translocation

The cutting and pasting of several DNA bases from one location to another.