Glossary

Actin: A protein that forms long filaments (or chains) and is important in maintaining cell shape. When it acts together with myosin, it produces cell movement.
Amino acids: The basic building blocks of proteins. There are 20 different types of amino acids that combine in different ways to form the proteins in living things. The amino acids are linked together according to the genetic information encoded in the organism's DNA.
Amplify: Make additional copies of a specific DNA fragment.
Apoptosis: Programmed cell death, the controlled suicide of certain cells for the good of the entire organism.
Autosome: A chromosome that is not involved in sex determination. The autosomes of males are similar to those of females. (Humans have 22 pairs of autosomes and two sex chromosomes, X and Y.)
Baker's yeast: See Budding yeast
Basal cell carcinoma: A common kind of skin cancer, usually caused by too much exposure to sunlight and easily curable by surgery.
Basal cell nevus syndrome (BCNS): A rare genetic disorder marked by proliferating skin cancers. Also known as Gorlin syndrome.
Base pairs: Pairs of complementary nitrogenous bases that interact to form each rung of DNA's double helix. Adenine (A) pairs with thymine (T); cytosine (C) pairs with guanine (G).
Budding yeast (baker's yeast, Saccharomyces cerevisiae): A yeast cell that reproduces by budding until the daughter cell reaches the same size as the mother cell, at which time the daughter cell splits off.
cDNA: See complementary DNA.
Caenorhabditis elegans: A microscopic roundworm, or nematode, used as a model organism to study genetics and development.
Caspase: An enzyme (a cysteine protease) that plays a key role in apoptosis.
Cell: The basic subunit of any living organism; the simplest unit that can exist as an independent living system.
Cell division: The process by which a cell grows and divides into two daughter cells.
Cell division cycle: The period from one cell division to the next. The cycle in which a growing cell passes several checkpoints, duplicates its DNA, and then goes into mitosis (divides into two identical cells.)
Chromosome: An organized structure located in the cell nucleus, consisting of a single molecule of DNA and many associated proteins. 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 about 40,000 genes from each parent.
Clone: A group of cells or molecules derived from a single ancestral cell or molecule.
Cloning: See Gene cloning.
Codon: A triplet of nucleotides that codes for an amino acid (or a stop signal.)
Complementary DNA (cDNA): A strand of DNA that can be synthesized in a test tube from a messenger RNA template after intron sequences have been spliced out.
Conserved DNA sequences: A sequence of DNA that has remained largely unchanged throughout evolution. Conserved DNA sequences are believed to be involved in important functions that are similar in different species.
Crystallography: See x-ray crystallography
Dopamine: A hormone-like substance that acts as a neurotransmitter, transmitting nerve signals from neuron to neuron.
Diploid: Containing two full sets of chromosomes, one inherited from the mother and one from the father.
Dominant: Refers to a characteristic that is apparent even when the relevant gene is present in only one copy. A dominant disorder can be inherited from only one parent.
DNA (deoxyribonucleic acid): The genetic material of living organisms; the substance of heredity. It is a large, double-stranded, helical molecule that contains genetic instructions for growth, development, and replication. The rungs of this double helix are made of base pairs.
DNA probe: A specific sequence of single-stranded DNA used to seek out a complementary sequence of single-stranded DNA. Probes are usually labelled radioactively or chemically to make them easier to detect, thus revealing the location of a target DNA sequence.
Drosophila melanogaster: A type of fruit fly used as a model organism to study genetics and development.
Embryonic stem (ES) cell: A very early embryonic cell that can either reproduce itself indefinitely or differentiate into a wide variety of specialized cells.
Enzyme: A protein (or, in some cases, an RNA molecule) that act as a catalyst, speeding up the rate at which a biochemical reaction proceeds.
Exon: A DNA sequence 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; in due time, these introns are spliced out of mRNA before translation.
Fission yeast: A yeast cell that reproduces by splitting down the center into two identical cells.
Gene: A sequence of DNA that represents a fundamental unit of heredity. Most genes code for RNA that is tranlated into protein, but some genes simply code for certain forms of RNA.
Gene cloning: Identifying, isolating and producing many identical copies of a gene.
Gene expression: The conversion of a gene's coded information into protein (or some form of RNA.)
Gene linkage map (also called linkage map): A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. (Genes that lie closer together on a chromosome are more likely to be inherited together since they are less likely to be separated during mitosis or meiosis.)
Gene targeting: A method scientists use to alter or turn off a particular gene in a chromosome.
Gene therapy: Treatment of a disease by introducing a new gene into a cell. The new gene may be used to replace a function that is missing because of a defective gene.
Gene transcription: The process by which a gene's DNA sequence is copied into RNA; the first step in gene expression.
Gene translation: The process by which transcribed messenger RNA, which carries a gene's instructions, directs the synthesis of proteins in a cell.
Genetic disease: A disease caused by a genetic mutation that is either inherited or arises spontaneously.
Genetic marker: A landmark that identifies a unique location on a chromosome.
Genetic screening: Testing of a population to identify people at risk for a specific genetic disease or at risk for transmitting such a disease to their children.
Geneticist: A scientist who studies genes, the basic units of heredity, and their variations.
Genome: The total genetic information of a particular organism. The normal human genome consists of 3 billion base pairs of DNA in each set of 23 chromosomes from one parent.
Germ cell (or sex cell): A reproductive cell, such as an egg or sperm cell. All germ cells are haploid.
Haploid: Containing only one set of chromosomes, either from the mother or the father.
Hermaphrodite: A creature with the sexual organs of both the male and the female.
Homeobox gene: A member of a group of genes involved in controlling the development of the front and back parts of the body. Genes in this group contain a conserved stretch of DNA called the homeobox and are nearly identical in all species.
Homolog: A sequence of DNA or protein that closely resembles another DNA or protein sequence in different organism.
Homologous recombination: A process by which one DNA segment can replace another DNA segment that has a similar sequence. Homologous recombination is used by researchers to create "knockout" mice in which the function of a specific gene is disrupted.
Human Genome Project: The international project that mapped and sequenced all the DNA in human beings.
"In-frame" triplets: Consecutive triplets of DNA bases (codons), each coding for one amino acid, that form an un-interrupted chain after a "start" signal and do not include any "stop" signal.
Introns: DNA sequences that interrupt the protein-coding sequences of a gene (exons) and are eventually spliced out. Only the exons are translated into protein. The function of introns is still being explored.
In vitro fertilization: Combination of an egg and a sperm outside of the mother's body to create an embryo.
"Knockout" mice: Experimental mice created by disrupting the function of a specific gene.
Leptin: A protein that acts as a signal to eat less.
Meiosis: The process of cell division (twice) in a germ cell progenitor, resulting in 4 daughter cells, each with a haploid set of chromosomes (23 chromosomes in humans).
Messenger RNA: RNA copied from a gene's DNA and carrying its instructions from the nucleus to the cytoplasm, where it directs the production of protein.
Microarray: A record of simultaneous activity by thousands of genes in a cell.
Microarrayer: A robot that can record the activity of thousands of genes simultaneously and show how it changes in varying circumstances.
Mitochondrion: An organelle (a membrane-bound body in a cell's cytoplasm) that is responsible for oxidation and has its own DNA.
Mitosis: The division of a cell into two daughter cells, each of which contains the complete diploid number of chromosomes (46 chromosomes in humans) and is genetically identical to the parent cell.
Model organism: A small organism that scientists can manipulate with ease in the lab.
Mutation: Any heritable change in DNA sequence. It can be an insertion or deletion of genetic information, or an alteration in the original genetic information.
Nematode: A worm with a long, cylindrical, unsegmented body, such as the model organism Caenorhabditis Elegans.
Neuropeptide: A chain of amino acids that functions in cell signaling in the nervous system.
Nucleotide: A building block of DNA or RNA, consisting of one nitrogenous base, one phosphate molecule, and one sugar molecule (deoxyribose in DNA, ribose in RNA).
Oligonucleotide: A short string of nucleotides; a single-stranded segment of DNA, often used as a probe to find a matching sequence of DNA or RNA.
Oncogene: A gene that can cause normal cells to be transformed into cancer cells by promoting cell growth.
Open reading frame (ORF): A series of DNA triplets that codes for amino acids without any stop signals and is potentially translatable into protein.
Peptide: Two or more amino acids linked together.
Petri dish: A small, round, shallow dish used in labs to culture cells in growth media.
Polymorphisms: Naturally occurring variations in DNA sequence. Polymorphisms are useful as genetic markers because they allow researchers to distinguish between DNA of different origins.
Positional cloning: Locating the gene for a specific trait by comparing the DNA of people who have that trait to the DNA of relatives who don't have the trait.
Promoter: A segment of DNA that acts as a controlling element in the expression of a gene.
Protein: A molecule composed of amino acids linked together in a particular order specified by a gene's DNA sequence. Proteins perform a wide variety of functions in the cell; these include serving as enzymes, structural components, or signaling molecules.
Proteome: All the proteins specified by the genome of a particular organism.
Proteomics: The study of all the proteins specified by a cell's DNA and of how these proteins interact.
Proto-oncogene: A normal gene that can be altered (either through mutation or through nearby insertion of viral DNA) to become an active oncogene.
Receptor: A protein located in a cell's surface membrane that binds with molecules outside the cell and, as a result of binding, changes its activity inside the cell.
Recessive: Refers to a characteristic that is apparent only when both copies of the gene encoding it are present—one from the mother and one from the father.
Recombinant DNA technology: Techniques for cutting apart, splicing together, and producing pieces of DNA from different sources.
RNA (ribonucleic acid): A single-stranded nucleic acid (similar to the double-stranded nucleic acid DNA) that contains the sugar ribose (DNA contains deoxyribose). Many forms of RNA, including messenger RNA, transfer RNA, and ribosomal RNA, are involved in protein synthesis.
Saccharomyces Cerevisiae: See Budding Yeast
Segmentation gene: A gene that is required for the establishment of segmentation (division into segments) in an embryo.
Serotonin: A hormone (5-hydroxytryptamine) that acts as a neurotransmitter, transmitting nerve signals from one neuron to another.
Sex cell: See Germ cell.
Sex chromosome: One of the chromosomes (X or Y) involved in sex determination. Normal human females have two X chromosomes in each cell, while normal males have one X and one Y.
Single-stranded DNA: DNA normally exists in two complementary strands that form a double helix, but it can be separated into two strands of single-stranded DNA. Separation becomes necessary when genes are being transcribed or when DNA is replicated prior to cell division.
Somatic cell: In multicellular organisms, a cell of the soma, or body tissues, as opposed to a cell of the germ line, or sex cell.
Spore: A highly resistant body that certain cells develop under conditions of stress and that may become dormant. It can develop into a new cell once conditions are again favorable for growth.
Sporulation: The formation of spores.
Transcription: See gene transcription.
Transgenic mice: Mice that have a foreign gene introduced into their cells.
Translation: See gene translation.
Tumor-suppressor gene: A gene that helps prevent the transformation of normal cells into cancer cells. When both copies of a tumor-suppressor gene are mutated in a cell, however, the result may be cancer.
X chromosome: One of the chromosomes involved in human sex determination. Normal human females have two X chromosomes in each somatic cell, while normal males have one X and one Y chromosome in each somatic cell.
X-linked: Refers to any gene found on the X chromosome or traits determined by such genes. Refers also to the specific mode of inheritance of such genes.
X-ray crystallography: A technique that enables scientists to decipher the 3-D structure of molecules. It depends on obtaining a crystal of the molecule and subjecting the crystal to x-rays. The structure of the molecule can then be deciphered from the pattern of x-ray scattering off atoms in the crystal.
Y chromosome: One of the chromosomes involved in human sex determination. Normal human males carry one Y chromosome and one X chromosome in each somatic cell, while normal females have two X chromosomes in each somatic cell.