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Pharmacogenomic Glossary of Terms

The following glossary includes some definitions or terms provided by the Genetics Home Reference of the U.S. National Library of Medicine.1

Allele – One of two or more forms of a single gene. Each person inherits two alleles for each gene, one from each parent.

Base pair – Two nucleotides on complementary DNA strands.

Chromosomes – A single strand of tightly coiled DNA that reside in pairs within the nucleus. Humans have 22 autosomal chromosomes (named as 1 to 22) and two sex chromosomes, X and Y.

Deletion – When one or more nucleotide pairs are lost from a DNA molecule.

Deoxyribonucleic acid (DNA) – Consists of nucleotides that reside in sequence along a backbone of deoxyribose sugar and phosphates. DNA contains the genetic instructions that program development and mature structure and function of individuals.

Duplication – The presence of an extra segment of DNA, resulting in redundant copies of a portion of a gene, an entire gene, or a series of genes.

Enzyme – A biological catalyst, usually a protein, that speeds up the rate of a specific chemical reaction. The body contains thousands of different enzyme molecules, each specific to a particular chemical reaction.

Exons – The expressed portion of a gene, exons contain the DNA sequences that are converted to mRNA during transcription, and thus determine the amino acid sequence in the protein product.

Gene – The physical and functional unit of inheritance, genes contain the instructions that help determine how the body develops and functions. Genes are passed down from parents to offspring and consist of hundreds to several million base pairs.

Genotype – Broadly, an individual’s collection of genes. In pharmacogenetics, the genotype is a particular DNA composition within a gene of interest. Its expression contributes to the individual’s observable traits, called a phenotype.

Genotypic screening – Testing that reveals the specific alleles inherited by an individual.

Gregor Mendel – Austrian monk who in 1866 published the basic laws of inheritance, even before the term “gene” had been coined. In his monastery garden, Mendel performed thousands of crosses with garden peas. Mendel explained his results as due to the inheritance of paired elementary units and their production of observable dominant and recessive traits in offspring.  Thus, he discovered the concepts of genotype and phenotype, and their relationship.

Heterozygosity – When two different alleles are present on the chromosome pair.

Homozygosity – When two identical alleles are present on the chromosome pair.

Insertion – A chromosomal abnormality in which additional DNA material from one chromosome is inserted into another DNA segment, most commonly disrupting the coding sequence.

Intron – DNA sequences in-between the exonic (coding) regions of a gene. Introns are not transcribed to mRNA but may contain other functional elements.

Locus – Designated location on a chromosome.

Messenger RNA (mRNA) – A ribonucleic acid (RNA) version of a gene that leaves the cell nucleus and moves to the cytoplasm.  During protein synthesis, the ribosome, a cytoplasmic organelle, moves along the mRNA and translates each three-base triplet into the corresponding amino acid.

Mutation – Any change in the nucleotide base sequence of a gene. Mutations are a key mechanism to evolution through their detrimental or advantageous effect on the fitness of the organism.

Nucleotide – Subunit of DNA consisting of a nitrogenous base, a phosphate group, and a deoxyribose sugar.

Pharmacodynamics – The biochemical and physiological effects of drugs, particularly those that define the drugs mechanism of action on the body.

Pharmacokinetics – The absorption, distribution, metabolism, and excretion (ADME) of bioactive drugs following their administration to higher organisms including man.

Pharmacogenetics – The identification of genetic variations and their association with variations in drug treatment response.

Pharmacogenomics – The incorporation of multiple pharmacogenetic results to develop a gene-based phenotypic characterization.  Pharmacogenomic uses include identifying responsive or side-effect prone patients in clinical practice and in drug development trials.

Polymorphism – A variant that has two or more alleles and is present at a frequency of at least 1% of the population. Polymorphisms are useful for genetic linkage analysis such as those used in pharmacogenetics.

Phenotype – The observable characteristics of an individual, such as body or tissue structure, behavior, or other measureable traits. The phenotype results from the expression of that individual’s genes and their interaction with environmental and internal factors.

Promoter – DNA sequence at the beginning of a gene that signals where RNA polymerase is to begin transcription.

Sequencing – A laboratory technique that determines the exact sequence of nucleotide bases in a DNA molecule. DNA sequence information is used to study how variations in genotypes impact gene function. DNA sequencing has become faster and cheaper since the completion of the Human Genome Project in 2000, when the first human genome was sequenced.

Single nucleotide polymorphism (SNP) – Pronounced “snip,” a single nucleotide locus with two or more naturally occurring alleles defined by a single base pair substitution.


1. Glossary. (n.d.). – Genetics Home Reference. Retrieved May 27, 2014, from https://ghr.nlm.nih.gov/glossary