Term	Definition
Allele	One of two or more versions of a gene; an individual inherits two alleles for each gene, one from each parent; if the two alleles are the same (e.g., CYP2C19*1/*1), the individual is homozygous for that gene; if the alleles are different (e.g., CYP2C19*1/*2), the individual is heterozygous
Gene	Basic physical and functional unit of heredity
Genotype	An individual's collection of genes
Pharmacogenetics (also called pharmacogenomics)	Study of how genes affect the way a person responds to medications; pharmacogenetics is being used to determine ahead of time the best drug or dose for an individual patient
Phenotype	Clinical presentation or observable characteristics of an individual with a particular genotype
Polymorphism	Natural variation in a gene, DNA sequence, or chromosome
Single nucleotide polymorphism	Type of polymorphism involving variation of a single base pair in the human genome
Star allele nomenclature	Common format used to represent variability of a specific gene; signified as gene symbol, *allele number /*allele number (e.g., CYP2C19*1/*2)