Diving Into the Gene Pool

GLOSSARY

Adenine (A): A base; one of the molecular components of D NA 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: Small molecules that form the building blocks of proteins.

Autosome: All chro mosomes except those involved in sex determination.

Bacteria: Tiny one-celled organisms.

Bases: The molecular building blocks of DNA and RNA: adenine, cytosine, guanine, thymine, and (in RNA only) uracil. In DNA, A attaches only to T, and C attaches only to G. In RNA, A attaches only to U, and C attaches only to G.

Base pair: Two of the building blocks of DNA held together by weak bonds. In a DNA molecule, adenine always bonds with thymine (A-T), and cytosine always bond s with guanine (C-G).

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 biologic al processes to manufacture products.

Cells: The basic units of life. All living organisms are a collection of cells. Chromosomes: The self-replicating genetic structures of cells.

Clone: A group of genetically identical cells or o rganisms 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.

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. Cytosine (C): A base; one of the molecular compon ents of DNA and RNA. Always bonds with guanine (C-G).

Diploid: Having a full set of genetic material consisting of paired chromosomes that contain one chromosome from each parent.

DNA (deoxyribonucleic acid): The long, spiralling m olecule that rchestrates the cell's daily operations and provides the genetic blueprint for the physical characteristics of all living organisms. When made up of two strands, the strands intertwine like a spiral staircase to form a structure called a doub le 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 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.

Domi nant gene: A gene which, when present on a chromosome, passes on a certain physical characteristic, thereby dominating over a recessive gene present on another chromosome. Double helix: A common name for DNA; it refers to the molecule's double-strande d, spiraling structure.

Electrophoresis: A method of separating large molecules-such as DNA fragments or proteins-from a mixture of similar molecules.

Enzyme: A protein that acts as a catalyst, speeding the rate at which a biochemi cal reaction proceeds but not altering the direction or nature of the reaction.

FISH (fluorescence in situ hybridization): A mapping technique that uses fluorescent tags to identify specific locations of chromosomes.

Gel: A dense net work of fine particles dispersed with water (Jell-O is a gel). Used to separate different-sized strands of DNA.

Gene: The fundamental unit of heredity.

Gene expression: The process by which genes express themselves: in the cell, ge ne expression results in the manufacture of proteins that determine an organism's characteristics.

Gene families: Groups of closely related genes that make similar products.

Gene mapping: Determining the relative positions of genes on a DNA molecule.

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 substituting the defective gene in the cells of a patient's body with a healthy gene.

Genetic engineering: The technology used to genetically manipulate living cells to produce new chemicals or perform new functions.

Genetic testing (o r genetic screening): A technique used to determine whether a person or organism has a certain gene.

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, 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 c haracteristics.

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 o f 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 specie s.

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 chromo some 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 se x 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 c ells 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 consisti ng 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.

P henotype: 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 ac ts 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 stri ng 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 b e 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 DN A.

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 stra nd 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 an d 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 c omponents of RNA. Bonds only with adenine (U-A).

Virus: A noncellular biological entity that can reproduce only within a host cell.


The Exploratorium, 3601 Lyon Street, San Francisco, CA 94123