Can’t find what you’re looking for? Feel free to email us. You can also try the Talking Glossary of Genetic Terms at the National Institutes of Health (NIH) or explore a comprehensive glossary at Nature Publishing Group.
Actionable: When information about a person’s genetic material is described as “actionable”, it means that we know enough about the particular genetic result to make a clinical decision or action.
Allele: A person typically has two versions of a gene. Each version is called an allele. For the majority of genes, one allele version is inherited from a person’s mother and one from their father. Sometimes one allele version may increase risk of developing a disease, while another may not. Other times both alleles are identical. If the alleles are the same, the individual is homozygous for that gene. If the alleles are different, the individual is heterozygous for that gene.
Autosome: An autosome is a chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes and one pair of sex chromosomes (46 chromosomes total). Autosomes are numbered according to their size from 1 (largest) to 22 (smallest).
Autosomal Dominant: Refers to a trait or disease that is expressed even if only one copy of a gene variant is present.
Autosomal Recessive: Refers to a trait or disease that is only expressed produced only when two copies of a gene variant are present.
Bases: Also known as nucleotides, bases are the basic components of DNA. They are denoted by the letters A (adenine), G (Guanine), C (cytosine) and T (thymine). The sequence of these bases forms the genetic code.
Carrier: An individual who has one mutated disease-causing gene mutation and one normal version of the gene.
Cell: The basic structural unit of all living organisms. Humans are composed of millions of cells. Each cell is enclosed by a membrane and has a nucleus which contains the genetic material (DNA) in the form of chromosomes.
Chromosome: A chromosome is a structure in the cell that carries genetic material. In humans, each chromosome contains hundred of genes, DNA sequence, and other genetic material. Human cells have 23 pairs of chromosomes (46 total). This includes 22 pairs of autosomes and one pair of sex chromosomes.
Dominant: Individuals typically receive two version of each gene (called an allele) – one from each parent. Alleles are often the same. If the alleles are different, the ‘dominant’ allele will be expressed, and the ‘recessive’ allele is not expressed. Sometimes, if two different alleles are present, they may both be expressed, as in the case of incomplete dominance, semi-dominance, or co-dominance.
DNA (deoxyribonucleic acid): The chemical molecule that makes up genes within chromosomes and is the basic material of heredity. It is made up of chemicals called nucleotide bases, linked together in a chain. Two chains of nucleotides twist around each other to form a double helix.
DNA Sequencing: The laboratory technique used to determine the pattern or order of the nucleotide bases in a strand of DNA.
Exome: The portion of the genome that contains genes.
Family History: A family history records medical information about a person and their family members. A family history can be used to help identify whether a person might be at an increased risk for developing certain genetic disorders.
Gene: A segment of DNA that contains the information for a specific characteristic or function.
Gene Expression: The process by which a gene is translated into a protein.
Genetic Information Nondiscrimination Act (GINA): A 2008 law that protects against discrimination based on genetic information in relation to your job and health insurance coverage. This law does not apply to life insurance or disability insurance.
Genome: The complete set of hereditary information carried by an individual or a cell, including the individual’s DNA.
Genome-Wide Association Study (GWAS): Compares groups of individuals by looking at where they differ at various points in their DNA sequence. You can read more about GWAS at the National Human Genome Research Institute.
Genotype: An individual’s genotype refers to their genetic characteristics. An individual’s genotype is different from their genome (their complete genetic material) in that it implies a measurement of how they differ genetically from a comparison group.
Heterozygous: A person typically has two versions of a gene, and each version is called an allele. For the majority of genes, one allele is inherited from a person’s mother and one from their father. When we say that a person is heterozygous for a gene, we mean the two versions of the allele are different. The opposite of this is ‘homozygous’, where both versions of the allele are the same.
Homozygous: A person typically has two versions of a gene, and each version is called an allele. For the majority of genes, one allele is inherited from a person’s mother and one from their father. When we say that a person is homozygous for a gene, we mean the two versions of the allele are the same. The opposite of this is ‘heterozygous’, where both versions of the allele are different.
Incidental Finding: A finding that is discovered in the course of clinical care or research testing that is unrelated to the reason for doing the test.
Karyotype: A karyotype is the complete set of chromosomes that an individual carries. It can also refer to the appearance of an individual’s chromosomes. In humans, the karyotype totals 46 chromosomes – 22 pairs of autosomes, and 1 pair of sex chromosomes.
Locus: In genetics, a locus refers to the specific location of a gene or section of DNA.
Medically Actionable: Refers to a disease or genetic variant that has options for improving your health or remaining healthier through changes in treatment or management of the condition.
Mitochondria: Small structures within cells that provide energy for the cell. Mitochondria have their own DNA, different from the DNA in the cell nucleus.
Mitochondrial Inheritance: The passing-on of mitochondrial DNA from women to their children.
Mutation: A change (variation) in a DNA sequence. Mutations can cause diseases or medical conditions, or result in no observable changes in traits or health.
Nucleotide: A nucleotide is a molecule that builds the DNA (or RNA) sequence. In DNA, there are four types of nucleotides, also called bases. These are: adenine (A), cytosine (C), guanine (G), and thymine (T), and combine to form long stretches of DNA sequence.
Oncogene: An oncogene is a mutated gene that leads to the development of a cancer.
P-Arm: The appearance of chromosomes is such that they have long arms and short arms. These arms join together at the center of the chromosome in an area called a centromere. The short arm of a chromosome is called the p-arm. The long arm is called the q-arm.
Personalized Medicine: A field of medicine that uses information about an individual’s genome to guide their healthcare.
Pharmacogenomics: A merging of the words ‘pharmacology’ and ‘genomics’ and refers to the use of information about a person’s genome to inform the drug treatments they should receive. Pharmacogenomics is also concerned with drug testing and drug development guided by genome research.
Phenotype: An individual’s observable characteristics, including their height/weight, blood type, or disease diagnosis.
Polymorphism: Natural variations in a DNA sequence that have no adverse effect on the individual, and that occur with fairly high frequency in the general population.
Protein: A complex organic molecule composed of one or more chains of amino acids. The order of the amino acids is determined by the sequence of bases in DNA. Some examples include enzymes, structural proteins, transport proteins and receptors.
Q-Arm: The appearance of chromosomes is such that they have long arms and short arms. These arms join together at the center of the chromosome in an area called a centromere. The long arm of a chromosome is called the q-arm. The short arm is called the p-arm.
Recessive: Individuals typically receive two version of each gene (called an allele) – one from each parent. Alleles are often the same. If the alleles are different, the ‘dominant’ allele will be expressed, and the ‘recessive’ allele is not expressed. Sometimes, if two different alleles are present, they may both be expressed, as in the case of incomplete dominance, semi-dominance, or co-dominance.
RNA (ribonucleic acid): A molecule that is transcribed from DNA by enzymes called RNA polymerases. The sequence of nucleotides in RNA is determined by the amino acid sequence in proteins when RNA is translated. RNA molecules can also act as catalysts or are involved in gene regulation.
SNP (single nucleotide polymorphism): Occurs when two individuals in the population differ by a single letter (or nucleotide) in the DNA sequence.
Syndrome: A group of characteristics and/or symptoms that occur together in a recognizable pattern.
Thioguanine: Thiopurines are drugs widely used to treat leukemias and autoimmune disorders such as inflammatory bowel disease (Crohn’s disease and ulcerative colitis) and arthritis. They are also used as an immunosuppressants after organ transplantation. Common thriopurines include azathioprine, mercaptopurine, and thioguanine.
Uracil: Uracil (U) is one of four chemical bases that builds RNA. The other three bases that make RNA are: adenine (A), cytosine (C), and guanine (G). Unlike these other three bases, uracil is not present in DNA, and is replaced by thymine (T).
Variant: An alteration in the normal sequence of a gene.
Whole Exome Sequencing: A laboratory method that reads all of the DNA bases in the parts of the genome that contain the instructions for makingT proteins and other functional elements of the DNA.
Whole Genome Sequencing: A laboratory method that reads the exact sequence of all DNA bases (A, C, G, and T) in a person’s entire genome.
X chromosome: The X chromosome is one of two sex chromosomes. The other sex chromosome is Y. Females have two X chromosomes in their cells (typically referred to as XX), while males have both an X and a Y chromosome (XY). Egg cells contain only an X chromosome, while sperm cells contain an X or a Y chromosome.
X-Linked: Refers to trait or disease caused by a mutation in a gene that is located on the X chromosome.
Y chromosome: The Y chromosome is one of two sex chromosomes. The other sex chromosome is Y. Females have two X chromosomes in their cells (typically referred to as XX), while males have both an X and a Y chromosome (XY). Egg cells contain only an X chromosome, and sperm cells contain an X or a Y chromosome.