Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Talking Glossary of Genetic Terms from National Human Genome Research Institute.

Activator (Ac): An autonomous transposable element in maize that also controls the movement of another transposon, Dissociator (DS).
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adenine: One of the four bases that make up DNA. Abbreviated with an 'A.'
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adenovirus: Adenoviruses contain double-stranded DNA and are unusually stable, allowing them to survive for prolonged periods outside of the body. Adenoviruses infect membranes of the respiratory tract, eyes, intestines, and urinary tract, and can cause respiratory infections and gastrointestinal upsets.
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agarose gel electophoresis: A matrix composed of a highly purified form of agar is used to separate larger DNA and RNA molecules ranging from 100 to 20,000 nucleotides.
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alkaptonuria: A rare inherited condition in which a person's urine turns a dark brownish-black color when exposed to air. A mutation on the HGD gene causes the condition.
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allele: An alternate version of a gene, e.g., Gregor Mendel's pea plants have flowers with two colors: white and reddish-purple. The flower color gene in this case has two alleles, one for white and the other for reddish-purple.
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amino acid: A class of molecules that are the building blocks of proteins. There are 20 different amino acids used to make up proteins.
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apoptosis (cell death): The natural process of programmed cell death as part of normal growth and development.
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Antennapedia: A homeotic mutation of Drosophila, where a pair of legs replaces the antenna.
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autosome: A chromosome that is not involved in sex determination.
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bacterium/bacteria: A single-cell prokaryotic organism. (see Escherichia coli)
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bacteriophage (phage or phage particle): A virus that infects bacteria. Altered forms are used as vectors for cloning DNA.
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base pairing: Discovery made by James Watson that was key in solving the structure of DNA. The bases that make up DNA pair with each other: A to T and G to C. The pairs are held together by hydrogen bonds
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BRCA1/BRCA2: Mutations in the BRCA1 and BRCA2 tumor suppressor genes are linked to inherited breast and ovarian cancer.
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cDNA library: A library composed of complementary copies of cellular mRNAs.
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cell cycle: The process of cell division and replication. In eukaryotic cells, the cell cycle has two periods: interphase, when the cell grows and duplicates its DNA (G1, S and G2 phases), and mitosis (M phase), when the cell splits into two daughter cells.
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Central Dogma: Theory developed by James Watson and Francis Crick to describe the process of protein production: DNA to RNA to protein.
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centromeres: Regions of chromosomes made up of non-coding, highly repetitive DNA. During mitosis this region connects the sister chromatids and attaches the spindle fibers that draw the separated chromosomes to opposite poles.
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chromatid: Each of the two daughter strands of a duplicated chromosome joined at the centromere during mitosis and meiosis.
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chromatin: Refers to the combined DNA and protein material that coils up to form chromosomes.
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chromosome: Chromosomes are packages of DNA found in the nucleus of cells. Humans have 46 chromosomes.
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clone: Refers to a replica. DNA molecules can be cloned using bacteria or viruses as hosts. A genetic clone can also refer to an organism that is a genetic copy of the original - produced using various in vitro techniques.
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codon: Three bases in a DNA sequence that encodes the type of amino acid to be placed in the protein. For example, the codon G-T-G signifies the amino acid valine.
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complementary DNA (cDNA): The matching strand of a DNA molecule to which its bases pair.
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conjugation: The transfer of genetic material between bacterial cells. DNA is passed from the donor cell to the recipient cell via direct cell-to-cell contact or a connection between two bacterial cells.
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crossing-over: The exchange of DNA sequences between chromatids of homologous chromosomes during meiosis.
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cytosine: One of the four bases that make up DNA. Abbreviated with a 'C.'
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DNA (Deoxyribonucleic acid): An organic acid and polymer composed of four nitrogenous bases — adenine, thymine, cytosine, and guanine — linked via intervening units of phosphate and the pentose sugar deoxyribose. DNA is the genetic material of most organisms and usually exists as a double-stranded molecule in which two antiparallel strands are held together by hydrogen bonds between adenine-thymine and cytosine-guanine.
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DNA array: DNA arrays (also known as microarrays or gene chips) can analyze patterns of gene expression and show how gene expression responds to external factors.
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DNA sequencing: Procedures for determining the nucleotide sequence of a DNA fragment.
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deletion: A mutation in DNA where a section of DNA is deleted. Some deletions have no effect while others can have a drastic effect, depending on how much DNA was deleted and whether the deletion was in a region of DNA that encoded a protein.
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density gradient centrifugation: A technique where cells, organelles or molecules can be separated using centrifugal force, depending on their size, shape and density.
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deoxyribonucleic acid: (See DNA)
dideoxynucleotide: A deoxynucleotide that lacks a 3' hydroxyl group, and is thus unable to form a 3'-5' phosphodiester bond necessary for chain elongation. Dideoxynucleotides are used in DNA sequencing and the treatment of viral diseases.
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diploid: The condition when the genome of an organism consists of two copies of each chromosome.
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Dissociator (Ds): A transposable element in maize, whose mobility is dependent on another element, Activator (Ac)
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dominant: A genetic trait or disorder is dominant when only one copy of the gene is necessary for the trait to develop. A recessive trait or disorder develops when two copies of the gene are inherited.
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double helix: Describes the coiling of the antiparallel strands of the DNA molecule, resembling a spiral staircase in which the paired bases form the steps and the sugar-phosphate backbones form the rails.
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Drosophilia melanogaster (fruit fly): An animal model system used to study genetics. Fruit flies are easy to maintain, have large numbers of offspring, grow quickly, and the genome is relatively straightforward to disrupt and introduce foreign genes.
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electrophoresis: The technique of separating charged molecules in a matrix to which is applied an electrical field.
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Escherichia coli (bacteria): A type of bacteria that inhabits the human colon. E. coli is one of the most important organisms in molecular genetics research, particularly in the area of recombinant DNA, as it serves as a host for plasmid and other cloning vectors.
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eugenics: An effort to breed better human beings by encouraging the reproduction of people with "good" genes and discouraging those with "bad" genes. The eugenics movement of the 19th century started in the United States and was eventually discredited.
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evolution: The long-term process through which a population of organisms accumulates genetic changes that enable its members to successfully adapt to environmental conditions and to better exploit food resources.
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exon: A section of a gene that contains the instructions for making a protein.
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gene: A portion of DNA that contains instructions for making a protein.
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gene expression: The process of producing a protein from its DNA- and mRNA-coding sequences.
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genetic (linkage) map: A linear map of the relative positions of genes along a chromosome. Distances are established by linkage analysis, which determines the frequency at which two gene loci become separated during chromosomal recombination.
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GeneChips®: A process of making and embedding specific DNA sequences onto a surface to be used for large-scale DNA analysis (see also DNA array).
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genetic code: The three-letter code that translates nucleic acid sequence into protein sequence (see also codon).
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genome: Refers to all the DNA of an organism - the entire genetic component.
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genotype: The structure of DNA that determines the expression of a trait (phenotype).
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germ line: The sequence of cells that have genetic material that may be passed on to offspring, e.g., zygote to gametocyte to sperm and egg cells. Germ line cells can reproduce indefinitely.
guanine: One of the four bases that make up DNA. Abbreviated with a 'G.'
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haploid: The chromosome number equal to one complete set of the genetic endowment of a eukaryotic organism.
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heterozygous: Possessing two different forms (alleles) of a gene, one inherited from each parent. Also known as a "gene carrier".
histone: Any of five related proteins, composed primarily of basic amino acids, which are the scaffold around which DNA is wound to form the chromatin structure of eukaryotic chromosomes.
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homeotic gene: Genes that control developmental patterns, determining where, when, and how body segments and structures develop. Alterations in these genes cause changes in patterns of body parts in animals and plants.
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homolog: Any member of a set of genes or DNA sequences from different organisms whose nucleotide sequences show a high degree of one-to-one correspondence.
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homozygous: Possessing two identical forms (alleles) of a gene, one inherited from each parent.
Human artificial chromosome (HAC): An artificial vector used to transfer or express large fragments of human DNA, similar to a yeast artificial chromosome (YAC) and bacterial artificial chromosome (BAC).
Human Genome Project: An international collaboration to sequence and annotate the entire human genome. The public part of the project was undertaken by various sequencing centers around the world with contributions from thousands of scientists. The private part of the project was undertaken by Celera Genomics.
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hybrid: The offspring of two parents differing in at least one genetic characteristic (trait). Also, heteroduplex DNA or DNA-RNA molecule.
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hybridization: The hydrogen bonding of complementary DNA and/or RNA sequences to form a duplex molecule.
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hydrogen bond: A relatively weak bond formed between a hydrogen atom (which is covalently bound to a nitrogen or oxygen atom) and a nitrogen or oxygen with an unshared electron pair.
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insertion: A mutation in DNA where a section of DNA is inserted. Some insertions have no effect while others can have a drastic effect, depending on how much DNA was inserted and whether the insertion was in a region of DNA that encoded a protein.
insulin: A peptide hormone secreted by the islets of Langerhans of the pancreas that regulates the level of sugar in the blood.
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interferon: A family of small proteins that stimulate viral resistance in cells.
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intron: A section of a gene that does not contain any instructions for making a protein. Introns separate exons (the coding sections of a gene) from each other.
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knockout: A gene that is prevented from functioning in an organism. "Knockout genes" can be used to study the unknown effects of a particular gene. A "knockout mouse" is a mouse that has had one or more genes "knocked out".
lac operon: An "operon" is the close arrangement of related genes and their common regulation. The lac operon controls the transport and metabolism of lactose in bacteria, and involves both positive and negative regulation.
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library: A collection of cells, usually bacteria or yeast, that have been transformed with recombinant vectors carrying DNA inserts from a single species.
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linkage: The frequency of coinheritance of a pair of genes and/or genetic markers, which provides a measure of their physical proximity to one another on a chromosome.
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mapping: Determining the physical location of a gene or genetic marker on a chromosome.
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marker: Used to identify cells, individuals or species, a marker is a gene or DNA sequence with a known chromosomal location.
meiosis: The reduction division process by which haploid gametes and spores are formed, consisting of a single duplication of the genetic material followed by two mitotic divisions.
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Mendelian inheritance: Rules describing the inheritance of characteristics, based around dominant and recessive patterns of inheritance. Mendel's First Law states that each gamete receives one copy of each parental allele; Mendel's Second Law states that alleles sort independently of one other during gamete formation.
messenger RNA (mRNA): A type of RNA involved in protein production. DNA is transcribed into mRNA, which is then translated into amino acids to form proteins.
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metaphase: A phase during the eukaryotic cell cycle when condensed chromosomes align in the middle of a dividing cell before the cell is separated into two daughter cells.
microarray: (see DNA array)
mitosis: The process of cell division during which somatic cells are made. In mitosis, one cell divides evenly to produce two daughter cells that have the same chromosome number.
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mitochondrion: An organelle that generates adenosine triphosphate (ATP), the main source of cellular energy. Mitochondria are also involved in cell signaling, differentiation, and cell cycle control and have their own independent genome, separate to the cell's nuclear DNA.
mitochondrial DNA: Mitochondria have their own independent genome, separate to a cell's nuclear DNA (mtDNA). The genome is usually circular, replicates independently and is comprised mainly of genes involved with production of adenosine triphosphate (ATP), the main source of cellular energy.
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model organism: A non-human organism, such as yeast, fruit fly or mouse, used to study biological phenomena, such as genetics. Model organisms share many genes, and biochemical and physiological processes with humans.
mutation: A change in the genetic code (the A's, C's, G's and T's) of a gene.
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Neurospora crassa (bread mold): A haploid model organism, most famously used by Beadle and Tatum to study metabolic pathways and propose the "one gene, one enzyme" hypothesis.
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nitrocellulose: A membrane used to immobilize DNA, RNA, or protein, which can then be probed with a labeled sequence or antibody.
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nitrogenous bases: The purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil) that comprise DNA and RNA molecules.
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nuclease: A class of enzymes that degrades DNA and/or RNA molecules by cleaving the phosphodiester bonds that link adjacent nucleotides.
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nuclein: The term used by Friedrich Miescher to describe the nuclear material he discovered in 1869, which today is known as DNA.
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nucleotide: A building block of DNA and RNA, consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group.
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nucleus: The membrane-bound region of a eukaryotic cell that contains the chromosomes.
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oncogene: A gene that contributes to cancer formation when mutated or inappropriately expressed.
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operator: A prokaryotic regulatory element that interacts with a repressor to control the transcription of adjacent structural genes.
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P53: A protein that acts as a "checkpoint" in cells, inducing either growth arrest, DNA repair, or cell death when the cell's DNA is damaged. Most cancer cells have mutations in the p53 protein.
pedigree: A diagram mapping the genetic history of a particular family.
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phage: (see bacteriophage)
phenotype: The expression of a trait based on the genetic makeup or genotype.
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phosphate: One of the components of DNA, the phosphodiester bonds form the sugar-phosphate backbone. Adenosine triphosphate (ATP) is also the main source of cellular energy.
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physical map: A map showing physical locations on a DNA molecule, such as restriction sites, RFLPs, and sequence-tagged sites.
plasmid: Circular pieces of DNA with bacterial components. These exist outside of and are replicated along with the bacterial chromosomes. There can be multiple plasmid copies in one bacterial cell. Foreign DNA can be added into plasmids using molecular enzymes to "cut" and "paste" the DNA.
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polylinker: A short DNA sequence containing several restriction enzyme recognition sites that is contained in cloning vectors.
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polymerase: An enzyme that catalyzes the addition of multiple subunits to a substrate molecule.
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polymerase chain reaction (PCR): A procedure that enzymatically amplifies a target DNA sequence of up to several thousand base pairs through repeated replication by DNA polymerase.
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polynucleotide: A DNA polymer composed of multiple nucleotides.
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polypeptide (protein): A polymer composed of multiple amino acid units linked by peptide bonds.
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primer: A short DNA or RNA fragment annealed to single-stranded DNA, from which DNA polymerase extends a new DNA strand to produce a duplex molecule.
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proinsulin: A polypeptide precursor of proinsulin, from which a 24-amino-acid signal peptide sequence is responsible for extracellular secretion.
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prokaryote: An organism whose cell(s) lacks a nucleus and other membrane-bound vesicles. Prokaryotes include all members of the Kingdom Monera.
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promoter: A region of DNA extending 150-300 bp upstream from the transcription start site that contains binding sites for RNA polymerase and a number of proteins that regulate the rate of transcription of the adjacent gene.
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protease: An enzyme that cleaves peptide bonds that link amino acids in protein molecules.
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protein: A polymer of amino acids linked via peptide bonds and which may be composed of two or more polypeptide chains.
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RNA (ribonucleic acid): An organic acid composed of repeating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester bonds.
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radioactive probe/tag: A fragment of DNA or RNA used to detect specific nucleotide sequences using the principle of DNA complementarity. The probe is "tagged" with a radioactive or fluorescent molecular marker to allow visualization.
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reading frame: A series of triplet codons beginning from a specific nucleotide. Depending on where one begins, each DNA strand contains three different reading frames.
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receptor: A protein molecule that binds one or more specific kinds of signaling molecules (ligands), which causes the receptor to change shape (conformation). This can then cause a loss or gain of protein activity and resultant cellular responses.
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recessive: A recessive genetic trait or disorder presents only when two copies of the gene are inherited. For a dominant trait or disorder one copy of the gene is necessary for the trait to develop.
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recognition sequence (site): A nucleotide sequence— composed typically of 4, 6, or 8 nucleotides— that is recognized by a restriction endonuclease. Type II enzymes cut (and their corresponding modification enzymes methylate) within or very near the recognition see Recognition sequence (site)
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recombination: A process whereby a section of DNA (or sometimes RNA) is broken and joined to another section of DNA, either naturally or artificially, allowing genetic variation. A common natural example is chromosomal crossover.
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repressor: A DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
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restriction endonuclease (enzyme): A class of endonucleases that cleaves DNA after recognizing a specific sequence.
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restriction fragment length polymorphism (RFLP): Differences in nucleotide sequence between alleles at a chromosomal locus result in restriction fragments of varying lengths detected by Southern analysis.
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restriction map: A physical map showing the locations of restriction enzyme recognition sites.
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retrovirus: A member of a class of RNA viruses that utilizes the enzyme reverse transcriptase to reverse copy its genome into a DNA intermediate, which integrates into the host-cell chromosome. Many naturally occurring cancers of vertebrate animals are caused by retroviruses.
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reverse transcriptase (RNA-dependent DNA polymerase): An enzyme isolated from retrovirus-infected cells that synthesizes a complementary (c)DNA strand from an RNA template.
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ribonucleic acid (RNA): An organic acid composed of repeating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester bonds.
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ribosomes: Structure made up of proteins and RNA that are the sites of protein production in the cell. Ribosomes decode messenger RNA (mRNA) and assemble amino acids into proteins based on the mRNA script.
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Saccharomyces cerevisiae: Brewer's yeast
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selectable marker: A gene whose expression allows one to identify cells that have been transformed or transfected with a vector containing the marker gene.
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semiconservative replication: During DNA duplication, each strand of a parent DNA molecule is a template for the synthesis of its new complementary strand. Thus, one half of a preexisting DNA molecule is conserved during each round of replication.
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sex chromosome: Sex chromosomes in the germ cells of most animals and some plants combine to determine the sex and sex-linked characteristics of an individual. Sex chromosomes are usually designated X and Y, with females being XX and males being XY in mammals.
sex linked: A pattern of inheritance when an allele is located on a sex chromosome and the phenotype of the allele is therefore related to the sex of the organism. As humans have more genes on the X chromosome than the Y chromosome, there are more human X-linked traits and diseases than Y-linked.
signal transduction: The biochemical events that conduct the signal of a hormone or growth factor from the cell exterior, through the cell membrane, and into the cytoplasm. This involves a number of molecules, including receptors, G proteins, and second messengers.
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splicing: Processing messenger RNA (mRNA) after transcription to remove introns and join exons to allow translation of mRNA into proteins.
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stem cells: Stem cells can differentiate into a range of specialized cells (they are "pluripotent"). Embryonic and adult stem cells can be grown artificially and have the potential to be used for medical therapies.
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sticky ends: A protruding, single-stranded nucleotide sequence produced when a restriction endonuclease cleaves off center in its recognition sequence.
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stop codon: Any of three mRNA sequences (UGA, UAG, UAA) that do not code for an amino acid and thus signal the end of protein synthesis.
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subtractive hybridization: A powerful technique to study gene expression in specific tissues or cell types at a specific stage of development.
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suicide gene: Genes that cause a cell to undergo cell death ("apoptosis"). These genes may be activated through a variety of signaling processes, with the p53 protein being a common "switch."
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supercoiling: DNA is tightly packaged within the nucleus by adding twists to create structural tension that is then relieved by supercoil structures. The DNA first wraps around histones to form a 10nm fiber, then this fiber is coiled into a 30nm fiber which is then coiled upon itself again.
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supernatant: The soluble liquid fraction of a sample after centrifugation or precipitation of insoluble solids.
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template: An RNA or single-stranded DNA molecule upon which a complementary nucleotide strand is synthesized.
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termination codon: (see stop codon)
thymine: One of the four bases that make up DNA, abbreviated with a "T." Thymine is replaced by uracil in RNA.
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trait: (see phenotype)
transcription: The process through which DNA is copied to messenger RNA (mRNA) for the production of protein.
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transfer RNA (tRNA): A specific class of RNA molecules that carry animo acids to the ribosomes for assembly into protein. There is a specific tRNA for each of the 20 amino acids.
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transformation: In prokaryotes, the natural or induced uptake and expression of a foreign DNA sequence— typically a recombinant plasmid in experimental systems. In higher eukaryotes, the conversion of cultured cells to a malignant phenotype— typically through infection by a tumor virus or transfection with an oncogene.
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transforming principle: The hypothesis, now proven, that bacteria are capable of transferring genetic information through transformation.
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transgenic: A vertebrate organism in which a foreign DNA gene (a transgene) is stably incorporated into its genome early in embryonic development. The transgene is present in both somatic and germ cells, is expressed in one or more tissues, and is inherited by offspring in a Mendelian fashion.
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translation: The process through which messenger RNA (mRNA) is used and decoded to produce protein. This happens at the protein-making factories of the cell called ribosomes.
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translocation: Breakage of a large segment of DNA from one chromosome, followed by the segment's attachment to a different chromosome.
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transposon: (transposable, or movable genetic element). A relatively small DNA segment that has the ability to move from one chromosomal position to another.
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trypsin: A proteolytic enzyme that hydrolyzes peptide bonds on the carboxyl side of the amino acids arginine and lysine.
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Ultrabithorax (Ubx): A homeotic gene that acts on the development of thoracic segments T2 and T3 in Drosophila.
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uracil: Found in RNA, this pyrimidine derivative pairs with adenine and replaces thymine during DNA transcription.
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vector: An autonomously replicating DNA molecule into which foreign DNA fragments are inserted and then propagated in a host cell.
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virus (see also retrovirus): An infectious particle composed of a protein capsule and a nucleic acid core, which is dependent on a host organism for replication.
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X-ray crystallography: The diffraction pattern of X-rays passing through a pure crystal of a substance used to deduce its atomic structure.
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X-ray diffraction: A technique used to determine the structure of molecules such as DNA. A stream of X-rays directed at a crystal diffract and scatter as they encounter atoms. The scattered rays interfere with each other and produce spots of different intensities that can be recorded on film.
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X-linked mutation: A genetic mutation located on the X chromosome, also referred to as sex-linked inheritance as there is a different pattern of inheritance between males and females.
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yeast: (see Saccharomyces cerevisiae)
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