Adenine (A): A base; one of the molecular components of DNA and RNA. Bonds with thymine (A-T) in DNA, and with uracil (A-U) in RNA.
Alleles: Alternative forms of a genetic characteristic.
Amino acids: The basic building blocks of proteins. There are 20 different amino acid types. Each protein consists of a different sequence of amino acids linked together according to the genetic information encoded in DNA.
Autosome: All chromosomes except those involved in sex determination. Humans have 22 pairs of autosomes and the X and Y sex chromosomes (XX for females, XY for males).
Bacteria: Tiny one-celled organisms.
Bases: Nitrogenous compounds that interact to form the molecular building blocks of DNA and RNA: adenine, cytosine, guanine, thymine, and (in RNA only) uracil.
Base pair: Two of the building blocks of DNA held together by hydrogen bonds. In a DNA molecule, adenine always bonds with thymine (A-T), and cytosine always bonds with guanine (C-G). In RNA, A binds to uracil (A-U).
Base sequence: The order of bases in a DNA molecule.
Base sequence analysis: A method, sometimes automated, for determining the sequence of bases in a strand of DNA.
Biotechnology: The use of biological processes to manufacture products.
C. elegans: A small worm that is used as a model organism to study genetics and development.
Cells: The basic units of life, the simplest unit that can exist as an independent living system. All living organisms are a collection of cells.
Chromosomes: The self-replicating genetic structures of cells, formed from DNA and protein, found in the cell nucleus. Each chromosome contains hundreds or thousands of the genes that form our hereditary blueprint. Humans have 23 pairs of chromosomes (each parent contributes one chromosome in each pair), containing a total of 50,000 to 100,000 genes from each parent.
Clone: A group of genetically identical cells or organisms that are descended from one parent. Identical twins are clones, as are colonies of bacteria that reproduce by simple cell division.
Cloning: The process of asexually producing a group of cells (clones), all genetically identical, from a single ancestor. Segments of DNA are cloned by insertion into a bacterial cell and then growing a colony of bacteria that all contain the inserted DNA.
Complementary DNA (cDNA): A single strand of DNA synthesized in the lab to complement the bases in a given strand of messenger RNA. Complementary DNA represents the parts of a gene that are expressed in a cell to produce a protein.
Complementary sequence: A sequence of bases that can form a double-stranded structure by matching base pairs. The complementary sequence to G-T-A-C, for instance, is C-A-T-G.
Conserved DNA sequences: Sequences of DNA that have remained largely unchanged throughout evolution. Conserved DNA sequences are believed to be involved in important functions that are similar in different species.
Cystic fibrosis (CF): A genetic disease involving a sticky buildup of mucus in the lungs (which makes breathing difficult and leads to infections), as well as pancreatic insufficiency (which leads to digestive problems). It is a recessive disease, occurring only when a child inherits two mutated copies of the CF gene--one from each parent.
Diploid: Having a full set of genetic material consisting of paired chromosomes. One of each pair of chromosomes comes from each parent.
DNA (deoxyribonucleic acid): The long, spiralling molecule that orchestrates the cell's daily operations and provides the genetic blueprint for the physical characteristics of all living organisms. When made up of two complementary strands, the strands intertwine like a spiral staircase to form a structure called a double helix. Subunits, called bases, are the rungs of the staircase. See also RNA.
DNA fingerprinting: A process which uses fragments of DNA to identify the unique genetic makeup of an individual.
DNA probe: A specific sequence of single-stranded DNA used to bind to a complementary DNA (or RNA) sequence of. Probes are usually labelled radioactively or chemically to make them easier to detect, thus revealing the target DNA sequence.
DNA replication: The use of existing DNA as a template for the synthesis of new DNA strands.
DNA sequence: The relative order of base pairs in any sample of DNA. See base sequence analysis.
DNA sequencing: Determining the order of bases in a segment of DNA.
Dominant gene: A gene which, when present on a chromosome, passes on a certain physical characteristic, even when the gene is present in only one copy. A dominant disorder can be inherited from only one parent.
Double helix: A common name for DNA; it refers to the molecule's double-stranded, spiraling structure.
Drosophila melanogaster: A type of fruit fly used as a model organism to study genetics and development.
Duchenne muscular dystrophy: A genetic disease that prevents muscles from developing properly in early childhood and may be crippling. Primarily affecting males, it is caused by a mutant gene on the X chromosome.
Electrophoresis: A method of separating large molecules-such as DNA fragments or proteins-from a mixture of similar molecules.
Embryonic stem (ES) cells: Early embryonic cells (usually mouse cells) that can be genetically manipulated by researchers and then implanted into embryos to produce transgenic animals (usually mice) with predetermined genetic mutations.
Enzyme: A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction. All cellular metablolism is controlled by enzymes.
Exon: A segment of a gene that contains instructions for making a protein. In many genes the exons are separated by "intervening" segments of DNA, known as introns, which do not code for proteins; these introns are removed by splicing to produce messenger RNA.
FISH (fluorescence in situ hybridization): A mapping technique that uses fluorescent tags to identify specific locations of chromosomes.
Gel: A dense network of fine particles dispersed with water (Jell-O is a gel). Used to separate different-sized strands of DNA.
Gene: A sequence of DNA that represents a fundamental unit of heredity. Most genes encode proteins, but some code for RNA molecules.
Gene cloning: Isolating a gene and producing many identical copies of it so that it can be studied in detail.
Gene expression: The process by which the information encoded in a the DNA sequence of a gene is first transcribed into RNA and then translated into protein, which then determines an organism's characteristics.
Gene families: Groups of closely related genes that make similar products.
Gene mapping (linkage maps): Determining the relative positions of genes on a DNA molecule. Genes that are generally inherited together are located close to each other on the chromosome and said to be linked.
Gene product: The biochemical material, either RNA or protein, resulting from expression of a gene.
Gene therapy: A newly evolving technique used to treat inherited genetic diseases. The medical procedure involves adding a healty gene into the cells of a patient's body, overcoming the effects of the defective gene.
Genetic engineering: The technology used to genetically manipulate living cells to produce new chemicals or perform new functions.
Genetic testing (or genetic screening): A technique used to determine whether a person (or other organism) has a disease causing allele of a certain gene. Identifies people at risk for a specific genetic disease or at risk for transmitting such a disease to their children.
Genetics: The study of the patterns of inheritance of specific traits.
Genome: All the genetic material in the chromosomes of a particular organism. The human genome consists of three billion bases of DNA, organized in about 100,000 genes on 23 chromosomes.
Genotype: The entire genetic identity of an individual, including alleles, or gene forms, that do not show as outward characteristics.
Guanine (G): A base; one of the molecular components of DNA and RNA. Always bonds with cytosine (G-C).
Haploid: A single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their sex cells. Compare to diploid.
Homologies: Similarities in DNA or protein sequences between individuals of the same species or among different species.
Human Genome Project (HGP): a worldwide project aimed at deciphering all the three billion bases of the human genome, including mapping and sequencing every gene. This information will help to more rapidly identify genes causing diseases in humans.
In vitro: Outside a living organism.
In vivo: Inside a living organism.
Karyotype: A photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type.
Mapping: See gene mapping, physical map.
Marker: An identifiable physical location on a chromosome (e.g., restriction enzyme cutting site, gene) whose inheritance can be monitored.
Meiosis: The production of sex cells, which are not genetically identical, through a series of cell divisions. Compare to mitosis.
Messenger RNA (mRNA): A single-stranded molecule of ribonucleic acid that directs protein production.
Mitosis: The production of cells that are genetically identical to the original cell. Compare to meiosis.
mRNA: See messenger RNA.
Mutation: A spontaneous or induced change in the DNA of a cell.
Nucleotide: A molecular subunit of DNA or RNA consisting of a base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. See DNA, base pair, RNA.
PCR: See polymerase chain reaction.
Phenotype: The outward physical characteristics of an organism.
Physical map: A map of the locations of identifiable landmarks on DNA, such as genes, or restriction enzyme cutting sites.
Polymerase: Polymerase is an enzyme that acts like a molecular assembly line to build new strands of DNA.
Polymerase chain reaction (PCR): A "biological copy machine": a method for making many copies of a specific DNA base sequence.
Polypeptide: A molecule made up of a string of amino acids. A protein is an example of a polypeptide.
Proteins: The active molecules in all cells. Proteins control biochemical reactions and determine the physical structure of organisms.
Recessive gene: A gene which must be present on both chromosomes in a pair to show outward signs of a certain characteristic.
Recombinant DNA: A form of DNA produced by splicing together segments of DNA from two or more organisms.
Restriction enzyme, endonuclease: A protein that recognizes specific, short sequences of DNA and cuts at those sites. See also Restriction enzyme cutting site.
Restriction enzyme cutting site: A specific sequence of DNA at which a particular restriction enzyme cuts the DNA.
Ribonucleic acid (RNA): A chemical cousin of DNA, RNA (ribonucleic acid) is responsible for translating the genetic code of DNA into proteins.
Ribosomal RNA (rRNA): A class of RNA found in the ribosomes of cells.
Ribosome: The small cellular structure in which RNA translates the genetic code into proteins.
RNA: See Ribonucleic acid.
Sequence: See Base sequence.
Sequencer: An apparatus used for deciphering the order of bases in a strand of DNA.
Sequencing: Determining of the order of bases in a DNA or RNA molecule.
Sex chromosomes: The X and Y chromosomes in human beings that determine the sex of an individual. Females have two X chromosomes; males have one X and one Y. Single strand: One half of a DNA double helix.
Somatic cells: Any cell in the body except sex cells.
Template: a single DNA strand that serves as pattern for building a new second strand.
Thymine (T): A base; one of the molecular components of DNA and RNA. Always bonds with adenine (T-A).
Transcription: The process by which DNA passes genetic information to RNA. Transcription is the first step in producing proteins.
Transfer RNA (tRNA): A class of RNA that carries amino acids into ribosomes and bonds with mRNA for protein production.
Translation: The process by which RNA makes proteins.
tRNA: See Transfer RNA.
Uracil (U): A base; one of the molecular components of RNA. Bonds only with adenine (U-A).
Virus: A noncellular biological entity that can reproduce only within a host cell.