Allele: One of two or more versions of a genetic sequence at a particular location in the genome.
Base pair (bp): Two nitrogenous bases paired together in double-stranded DNA by weak bonds; specific pairing of these bases (adenine with thymine and guanine with cytosine) facilitates accurate DNA replication; when quantified (e.g., 8 bp), bp refers to the physical length of a sequence of nucleotides.
Complex condition: A condition caused by the interaction of multiple genes and environmental factors. Examples of complex conditions, which are also called multifactorial diseases, are sepsis, cancer, and heart disease.
DNA: Deoxyribonucleic acid, the molecules inside cells that carry genetic information and pass it from one generation to the next.
Exon: The portion of a gene that encodes amino acids.
Gene: The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or an RNA molecule).
Gene chip: A solid substrate, usually silicon, onto which a microscopic matrix of nucleotides is attached. Gene chips, which can take a wide variety of forms, are frequently used to measure variations in the amount or sequence of nucleic acids in a sample.
Genome: The entire set of genetic instructions found in a cell. In humans, the genome consists of 23 pairs of chromosomes, found in the nucleus, as well as a small chromosome found in the cells’ mitochondria.
Genome-wide association study (GWAS): An approach used in genetics research to look for associations between many (typically hundreds of thousands) specific genetic variations (most commonly SNPs) and particular diseases.
Genotype: A person’s complete collection of genes. The term can also refer to the two alleles inherited for a particular gene.
Haplotype: A set of DNA variations, or polymorphisms, that tend to be inherited together. A haplotype can refer to a combination of alleles or to a set of SNP found on the same chromosome.
HapMap: The nickname of the International HapMap (short for “haplotype map”) Project, an international venture that seeks to map variations in human DNA sequences to facilitate the discovery of genetic variants associated with health. The HapMap describes common patterns of genetic variation among people.
Human Genome Project: An international project completed in 2003 that mapped and sequenced the entire human genome.
Microarray: A technology used to study many genes at once. Thousands of gene sequences are placed in known locations on a glass slide. A sample containing DNA or RNA is deposited on the slide, now referred to as a gene chip. The binding of complementary base pairs from the sample and the gene sequences on the chip can be measured with the use of fluorescence to detect the presence and determine the amount of specific sequences in the sample.
Mutation: A change in a DNA sequence. Germ-line mutations occur in the eggs and sperm and can be passed on to offspring, whereas somatic mutations occur in body cells and are not passed on.
Pharmacogenomics: The branch of pharmacology that deals with the influence of genetic variation on drug response in patients by correlating gene expression or SNPs with a drug’s efficacy or toxicity. By doing so, pharmacogenomics aims to develop rational means to optimize drug therapy, with respect to the patients’ genotype, to ensure maximum efficacy with minimal adverse effects.
Phenotype: The observable traits of an individual person, such as height, eye color, and blood type. Some traits are largely determined by genotype, whereas others are largely determined by environmental factors.
Point mutation: An alteration in DNA sequence caused by a single-nucleotide base change, insertion, or deletion.
Ribonucleic acid (RNA): The molecule synthesized from the DNA template; contains the sugar ribose instead of deoxyribose, which is present in DNA; three types of RNA exist including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
Single-nucleotide polymorphism (SNP): A single-nucleotide variation in a genetic sequence; a common form of variation in the human genome.
Systems biology: Research that takes a holistic rather than reductionist approach to understanding organism functions.
Transcription: The synthesis of an RNA copy from a sequence of DNA (a gene); a first step in gene expression.
Translation: During protein synthesis, the process through which the sequence of bases in a molecule of messenger RNA is read in order to create a sequence of amino acids.