Glossary
Allele: One of a number of alternative forms of the same gene.
Base: A basic component of DNA. There are four bases that form the rungs of the DNA double helix: adenine (A), thymine (T), cytosine (C) and guanine (G). The order of these bases determines a person’s genetic code. Bases are sometimes used interchangeably with nucleotides.
Cell: The building blocks of the body. Cells provide structure, take in nutrients from food, and perform all the body’s important functions. Almost all of the body’s cells contain a complete copy of a person’s unique genetic code.
Codon: A sequence of three bases (A, C, G, and T) that corresponds to a specific amino acid or a stop codon.
Chromosome: A structure found in most cells that contains all of a person’s DNA, tightly wound around proteins called histones.
Consanguineous: Having a common ancestor. For example, parents who are also first cousins.
DNA: Deoxyribonucleic acid – the substance that contains a person’s unique genetic instructions
Gene: A section of DNA that is the basis of inheritance. Each gene contains the code for a particular molecule (usually a protein) that the body needs to function properly.
Genetic variant: A change in a person’s DNA sequence.
Germline variant: A variant present in egg or sperm cells that is able to be passed from parent to child
Heterozygous: If a person is described as being heterozygous for a particular genetic variant, this means that the variant only affects one copy of a gene. People who are heterozygous for a dominant condition will be affected, while people heterozygous for a recessive condition will be able to pass that condition on to their children, but usually not be affected themselves.
Homozygous: A person is homozygous for a particular genetic variant when that variant is present in both copies of a gene.
Inversion: Two breaks in the chromosome allow for a chromosome segment to be removed and flipped 180 degrees before rejoining the broken ends. This reverses the DNA sequence (order of bases) within the chromosome.
Mitochondrial DNA (mtDNA): Mitochondria are structures in cells that produce energy. They contain a small amount of DNA (mtDNA) which codes for 37 genes – these are required for normal mitochondria function. Other genes necessary for mitochondrial function are also found elsewhere in a person’s genome. The mitochondria, and thus mitochondrial DNA, are passed only from mother to offspring.
Nucleotide: A basic building block for DNA and RNA. A nucleotide is composed of a base, phosphate group and sugar molecule (deoxyribose in DNA). Nucleotides are sometimes used interchangeably with bases.
Pathogenic variant: Variants that have proven to be associated with a disease. These type of variants are generally rare in populations.
Somatic variant: A variant acquired at some point during a person’s lifetime that is not able to be passed from parent to child. These variants are not found in the egg or sperm cells.
Stop codon: A codon that instructs for termination of a polypeptide chain (protein) during translation.
Transcription: Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA
Translation: The process of reading codons in the messenger RNA sequence to produce a chain of amino acids (protein). This step occurs after transcription.
Translocation: A chromosome segment is broken off and reattached to a different chromosome
