Abiotic stress. Outside (nonliving) factors which can cause
harmful effects to plants, such as soil conditions, drought,
Abzyme. See Catalytic antibody.
Adaptive radiation. The evolution of new species or sub-
species to fill unoccupied ecological niches.
Aerobe. A microorganism that grows in the presence of
oxygen. See Anaerobe.
Agarose gel electrophoresis. A matrix composed of a highly
purified form of agar that is used to separate larger DNA
and RNA molecules ranging 20,000 nucleotides. (See
Alleles. Alternate forms of a gene or DNA sequence, which
occur on either of two homologous chromosomes in a diploid
organism. (See DNA polymorphism.)
Alternative mRNA splicing. The inclusion or exclusion of
different exons to form different mRNA transcripts. (See
Amino acid. Any of 20 basic building blocks of proteins--
composed of a free amino (NH2) end, a free carboxyl (COOH)
end, and a side group (R).
Ampicillin (beta-lactamase). An antibiotic derived from
penicillin that prevents bacterial growth by interfering
with cell wall synthesis.
Amplify. To increase the number of copies of a DNA sequence,
in vivo by inserting into a cloning vector that replicates
within a host cell, or in vitro by polymerase chain reaction
Anaerobe. An organism that grows in the absence of oxygen.
Anneal. The pairing of complementary DNA or RNA sequences,
via hydrogen bonding, to form a double-stranded
polynucleotide. Most often used to describe the binding of a
short primer or probe.
Antibiotic. A class of natural and synthetic compounds that
inhibit the growth of or kill other microorganisms. (See
Antibiotic resistance, Bacteriocide, Bacteriostat.)
Antibiotic resistance. The ability of a microorganism to
produce a protein that disables an antibiotic or prevents
transport of the antibiotic into the cell.
Antibody. An immunoglobulin protein produced by B-
lymphocytes of the immune system that binds to a specific
antigen molecule. (See monoclonal antibodies, polyclonal
Anticodon. A nucleotide base triplet in a transfer RNA
molecule that pairs with a complementary base triplet, or
codon, in a messenger RNA molecule. See Codon, Messenger
Antigen. Any foreign substance, such as a virus, bacterium,
or protein, that elicits an immune response by stimulating
the production of antibodies. (See Antigenic determinant,
Antigenic determinant. A surface feature of a microorganism
or macromolecule, such as a glycoprotein, that elicits an
Antigenic switching. The altering of a microorganism's
surface antigens through genetic rearrangement, to elude
detection by the host's immune system.
Antimicrobial agent. Any chemical or biological agent that
harms the growth of microorganisms.
Anti-oncogene. See Recessive oncogene.
Antisense RNA. A complementary RNA sequence that binds to a
naturally occurring (sense) mRNA molecule, thus blocking its
translation. (See RNA.)
Asexual reproduction. Nonsexual means of reproduction which
can include grafting and budding.
Autosome. A chromosome that is not involved in sex de-
beta-DNA. The normal form of DNA found in biological
systems, which exists as a right-handed helix.
beta-Lactamase. Ampicillin resistance gene. (See Selectable
Bacillus. A rod-shaped bacterium.
Bacillus thuringiensis (Bt). A bacterium that kills
insects; a major component of the microbial pesticide
Backcross. Crossing an organism with one of its parent
Bacteriocide. A class of antibiotics that kills bacterial
Bacteriophage (phage or phage particle). A virus that in-
fects bacteria. Altered forms are used as vectors for
Bacteriostat. A class of antibiotics that prevents growth of
Bacterium. A single-celled, microscopic prokaryotic
organism: a single cell organism without a distinct
Base pair (bp). A pair of complementary nitrogenous bases in
a DNA molecule--adenine-thymine and guanine-cytosine. Also,
the unit of measurement for DNA sequences.
Bioaugmentation. Increasing the activity of bacteria that
decompose pollutants; a technique used in bioremediation.
Biodiversity. The wide diversity and interrelatedness of
earth organisms based on genetic and environmental factors.
Bioenrichment. Adding nutrients or oxygen to increase
microbial breakdown of pollutants.
Biofilms. See Microbial mats.
Biologics. Agents, such as vaccines, that give immunity to
diseases or harmful biotic stresses.
Biomass. The total dry weight of all organisms in a
particular sample, population, or area.
Bioremediation. The use of microorganisms to remedy
environmental problems. See Bioaugmentation, Bioenrichment.
Biotechnology. The scientific manipulation of living organ-
isms, especially at the molecular genetic level, to produce
useful products. Gene splicing and use of recombinant DNA
(rDNA) are major techniques used.
Biotic stress. Living organisms which can harm plants ,
such as viruses, fungi, and bacteria, and harmful insects.
See Abiotic stress.
bP. See Base pair.
Bt. See Bacillus thuringiensis.
Capsid. See Coat protein.
Carcinogen. A substance that induces cancer.
Carcinoma. A malignant tumor derived from epithelial tissue,
which forms the skin and outer cell layers of internal
Catalyst. A substance that promotes a chemical reaction by
lowering the activation energy of a chemical reaction, but
which itself remains unaltered at the end of the reaction.
(See Catalytic antibody, Catalytic RNA.)
Catalytic antibody (abzyme). An antibody selected for its
ability to catalyze a chemical reaction by binding to and
stabilizing the transition state intermediate.
Catalytic RNA (ribozyme). A natural or synthetic RNA
molecule that cuts an RNA substrate.
Cation. A positively charged ion.
cDNA. DNA synthesized from an RNA template using reverse
cDNA library. A library composed of complementary copies of
cellular mRNAs. (See Library.)
Cellular oncogene (proto-oncogene). A normal gene that when
mutated or improperly expressed contributes to the
development of cancer. (See Oncogene.)
Centers of origin. Usually the location in the world where
the oldest cultivation of a particular crop has been
Central dogma. Francis Crick's seminal concept that in
nature genetic information generally flows from DNA to RNA
Centrifugation. Separating molecules by size or density
using centrifugal forces generated by a spinning rotor. G
forces of several hundred thousand times gravity are
generated in ultracentrifugation. (See Density gradient
Centromere. The central portion of the chromosome to which
the spindle fibers attach during mitotic and meiotic
Chemotherapy. A treatment for cancers that involves ad-
ministering chemicals toxic to malignant cells.
Chloramphenicol. An antibiotic that interferes with protein
Chromatid. Each of the two daughter strands of a duplicated
chromosome joined at the centromere during mitosis and
Chromosome. A single DNA molecule, a tightly coiled strant
of DNA, condensed into a compact structure in vivo by
complexing with accessory histones or histone-like proteins.
Chromosomes exist in pairs in higher eukaryotes. (See
Chromosome walking. Working from a flanking DNA marker,
overlapping clones are successively identified that span a
chromosomal region of interest. (See Chromosome.)
Cistron. A DNA sequence that codes for a specific
polypeptide; a gene. See DNA, Gene.
Clone. An exact genetic replica of a specific gene or an
entire organism. See Cloning.
Cloning. The mitotic division of a progenitor cell to give
rise to a population of identical daughter cells or clones.
(See Directional cloning, Megabase cloning, Molecular
Coat protein (capsid). The coating of a protein that
enclosed the nucleic acid core of a virus.
Codon. A group of three nucleotides that specifies addition
of one of the 20 amino acids during translation of an mRNA
into a polypeptide. Strings of codons form genes and
strings of genes form chromosomes. (See Initiation codon,
Coenzyme (cofactor). An organic molecule, such as a vitamin,
that binds to an enzyme and is required for its catalytic
Cofactor. See Coenzyme.
Colony. A group of identical cells (clones) derived from a
single progenitor cell.
Commensalism. The close association of two or more
dissimilar organisms where the association is advantageous
to one and doesn't affect the other(s). See Parasitism,
Competency. An ephemeral state, induced by treatment with
cold cations, during which bacterial cells are capable of
uptaking foreign DNA.
Complementary DNA or RNA. The matching strand of a DNA or
RNA molecule to which its bases pair. (See DNA, RNA.)
Complementary nucleotides. Members of the pairs
adenine-thymine, adenine-uracil, and guaninecytosine that
have the ability to hydrogen bond to one another. (See
Concatemer. A DNA segment composed of repeated sequences
linked end to end.
Conjugation. The joining of two bacteria cells when genetic
material is transferred from one bacterium to another.
Constitutive promoter. An unregulated promoter that allows
for continual transcription of its associated gene. (See
Contiguous (contig) map. The alignment of sequence data from
large, adjacent regions of the genome to produce a
continuous nucleotide sequence across a chromosomal region.
Copy DNA. See cDNA.
Cross-hybridization. The hydrogen bonding of a single-
stranded DNA sequence that is partially but not entirely
complementary to a singlestranded substrate. Often, this
involves hybridizing a DNA probe for a specific DNA sequence
to the homologous sequences of different species.
Cross-pollination. Fertilization of a plant from a plant
with a different genetic makeup.
Crossing-over. The exchange of DNA sequences between
chromatids of homologous chromosomes during meiosis.
Culture. A particular kind of organism growing in a
Cyclic AMP (cyclic adenosine monophosphate). A second
messenger that regulates many intracellular reactions by
transducing signals from extracellular growth factors to
cellular metabolic pathways.
Cytogenetics. Study that relates the appearance and behavior
of chromosomes to genetic phenomenon.
Dalton. A unit of measurement equal to the mass of a
hydrogen atom, 1.67 x 10E-24 gram/L (Avogadro's number).
Death phase. The final growth phase, during which nutrients
have been depleted and cell number decreases. (See Growth
Denature. To induce structural alterations that disrupt the
biological activity of a molecule. Often refers to breaking
hydrogen bonds between base pairs in double-stranded nucleic
acid molecules to produce in single-stranded polynucleotides
or altering the secondary and tertiary structure of a
protein, destroying its activity.
Density gradient centrifugation. High-speed centrifugation
in which molecules "float" at a point where their density
equals that in a gradient of cesium chloride or sucrose.
Deoxyribonucleic acid. See DNA, nuclease.
Diabetes. A disease associated with the absence or reduced
levels of insulin, a hormone essential for the transport of
glucose to cells.
Dideoxynucleotide (didN). 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. (See Nucleotide.)
didN. See Dideoxynucleotide.
Digest. To cut DNA molecules with one or more restriction
Diploid cell. A cell which contains two copies of each
chromosome. See Haploid cell.
Directional cloning. DNA insert and vector molecules are
digested with two different restriction enzymes to create
noncomplementary sticky ends at either end of each
restriction fragment. This allows the insert to be ligated
to the vector in a specific orientation and prevents the
vector from recircularizing. (See Cloning.)
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 adeninethymine
and cytosine-guanine. (See b-DNA, cDNA, Complementary DNA
or RNA, DNA polymorphism, DNA sequencing, Double-stranded
complementary DNA, Duplex DNA, Z-DNA.)
DNA diagnosis. The use of DNA polymorphisms to detect the
presence of a disease gene.
DNA fingerprint. The unique pattern of DNA fragments
identified by Southern hybridization (using a probe that
binds to a polymorphic region of DNA) or by polymerase chain
reaction (using primers flanking the polymorphic region).
DNA ligase. See Ligase.
DNA polymerase. See Polymerase.
DNA polymorphism. One of two or more alternate forms
(alleles) of a chromosomal locus that differ in nucleotide
sequence or have variable numbers of repeated nucleotide
units. (See Allele.)
DNA polymerase. See Polymerase.
DNA sequencing. Procedures for determining the nucleotide
sequence of a DNA fragment.
DNase (deoxyribonuclease). See Nuclease.
Dominant. An allele is said to be dominant if it expresses
its phenotype even in the presence of a recessive allele.
See Allele, Phenotype, Recessive.
Dominant gene. A gene whose phenotype is when it is present
in a single copy.
Dominant(-acting) oncogene. A gene that stimulates cell
proliferation and contributes to oncogenesis when present in
a single copy. (See Oncogene.)
Dormancy. A period in which a plant does not grow, awaiting
necessary environmental conditions such as temperature,
moisture, nutrient availability.
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.
Double-stranded complementary DNA (dscDNA). A duplex DNA
molecule copied from a cDNA template.
Downstream. The region extending in a 3' direction from a
dscDNA. See double-stranded complementary DNA.
Duplex DNA. Double-stranded DNA.
Ecology. The study of the interactions of organisms with
their environment and with each other.
Ecosystem. The organisms in a plant population and the
biotic and abiotic factors which impact on them. See
abiotic factors; Biotic factors.
Electrophoresis. The technique of separating charged mol-
ecules in a matrix to which is applied an electrical field.
(See Agarose gell electrophoresis, Polycrylamide gell
Electroporation. A method for transforrning DNA, especially
useful for plant cells, in which high voltage pulses of
electricity are used to open pores in cell membranes,
through which foreign DNA can pass.
Encapsidation. Process by which a virus' nucleic acid is
enclosed in a capsid. See Coat protein.
Endonuclease. See Nuclease.
Endophyte. An organism that lives inside another.
Environmental Protection Agency (EPA). The U.S. regulatory
agency for biotechnology of microbes. The major laws under
which the agency has regulatory powers are the Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA); and the
Toxic Substances Control Act (TSCA).
Enzymes. Proteins that control the various steps in all
EPA. See Environmental Protection Agency.
Escherichia coli. A commensal bacterium inhabiting the human
colon that is widely used in biology, both as a simple model
of cell biochemical function and as a host for molecular
Ethidium bromide. A fluorescent dye used to stain DNA and
RNA. The dye fluoresces when exposed to UV light.
Eukaryote. An organism whose cells possess a nucleus and
other membrane-bound vesicles, including all members of the
protist, fungi, plant and animal kingdoms; and excluding
viruses, bacteria, and blue-green algae. See Prokaryote.
Evolution. The long-term process through which a population
of organisms accumulats genetic changes that enable its
members to successfully adapt to environmental conditions
and to better exploit food resources.
Exon. A DNA sequence that is ultimately translated into
protein. See DNA.
Exonuclease. See Nuclease.
Express. To translate a gene's message into a molecular
Expression library. (See Library.)
FDA. See Food and Drug Administration.
Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).
See Environmental Protection Agency.
Federal Plant Pest Act (PPA). See U.S. Department of
Federal Seed Act. See U.S. Department of Agriculture.
FIFRA. The Federal Insecticide, Fungicide, and Rodenticide
Act. See Environmental Protection Agency.
Flanking region. The DNA sequences extending on either side
of a specific locus or gene.
Food and Drug Administration (FDA). The U.S. agency
responsible for regulation of biotechnology food products.
The major laws under which the agency has regulatory powers
include the Food, Drug, and Cosmetic Act; and the Public
Health Service Act.
Food, Drug, and Cosmetic Act. See Food and Drug
Fungicide. An agent, such as a chemical, that kills fungi.
Fungus. A microorganism that lacks chlorophyll.
Fusion gene. A hybrid gene created by joining portions of
two different genes (to produce a new protein) or by joining
a gene to a different promoter (to alter or regulate gene
Gamete. A haploid sex cell, egg or sperm, that contains a
single copy of each chromosome.
GEM. A genetically engineered microorganism.
Gene. A locus on a chromosome that encodes a specific
protein or several related proteins. It is considered the
functional unit of heredity. (See Dominant gene, Fusion
gene, Gene amplification, Gene expression, Gene flow, Gene
pool, Gene splicing, Gene translocation, Recessive gene,
Gene amplification. The presence of multiple genes.
Amplification is one mechanism through which proto-oncogenes
are activated in malignant cells.
Gene cloning. The process of synthesizing multiple copies
of a particular DNA sequence using a bacteria cell or
another organism as a host. See DNA, Host.
Gene expression. The process of producing a protein from its
DNA- and mRNA-coding sequences.
Gene flow. The exchange of genes between different but
(usually) related populations.
Gene frequency. The percentage of a given allele in a
population of organisms. See Allele.
Gene insertion. The addition of one or more copies of a
normal gene into a defective chromosome.
Gene linkage. The hereditary association of genes located
on the same chromosome.
Gene modification. The chemical repair of a gene's
defective DNA sequence. See DNA.
Gene pool. The totality of all alleles of all genes of all
individuals in a particular population.
Gene splicing. Combining genes from different organisms
into one organism. See recombinant DNA.
Gene translocation. The movement of a gene fragment from one
chromosomal location to another, which often alters or
Genetic assimilation. Eventual extinction of a natural
species as massive pollen flow occurs from another related
species and the older crop becomes more like the new crop.
See Gene flow.
Genetic code. The three-letter code that translates nucleic
acid sequence into protein sequence. The relationships
between the nucleotide base-pair triplets of a messenger RNA
molecule and the 20 amino acids that are the building blocks
of proteins. See Base pair, Nucleic acid, Nucleotide.
Genetic disease. A disease that has its origin in changes to
the genetic material, DNA. Usually refers to diseases that
are inherited in a Mendelian fashion, although noninherited
forms of cancer also result from DNA mutation.
Genetic drift. Random variation in gene frequency from one
generation to another.
Genetic engineering. The manipulation of an organism's
genetic endowment by introducing or eliminating specific
genes through modern molecular biology techniques. A broad
definition of genetic engineering also includes selective
breeding and other means of artificial selection.
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. (See Mapping.)
Genetic marker. A gene or group of genes used to "mark" or
track the action of microbes.
Genome. The genetic complement contained in the chromosomes
of a given organism, usually the haploid chromosome state.
Genomic library. A library composed of fragments of genomic
DNA. (See Library.)
Genotype. The structure of DNA that determines the
expression of a trait. See Phenotype.
Genus. A category including closely related species.
Interbreeding between organisms within the same category can
GEO. Genetically engineered organism.
Germ cell. Reproductive cell. See Somatic cell.
Germ cell (germ line) gene therapy. The repair or re-
placement of a defective gene within the gamete-forming
tissues, which produces a heritable change in an organism's
GMO. Genetically modified organism.
Green revolution. Advances in genetics, petrochemicals, and
machinery that culminated in a dramatic increase in crop
productivity during the third quarter of the 20th century.
Growth curve. See Growth phase.
Growth factor. A serum protein that stimulates cell division
when it binds to its cell-surface receptor.
Growth phase (curve). The characteristic periods in the
growth of a bacterial culture, as indicated by the shape of
a graph of viable cell number versus time. (See Death
phase, Lag phase, Logarithmic phase, Stationary phase.)
Haploid cell. A cell containing only one set, or half the
usual (diploid) number, of chromosomes.
Hemophilia. An X-linked recessive genetic disease, caused by
a mutation in the gene for clotting factor VIII (hemophilia
A) or clotting factor IX (hemophilia B), which leads to
abnormal blood clotting.
Herbicide. Any substance that is toxic to plants; usually
used to kill specific unwanted plants.
Heterochromatin. Dark-stained regions of chromosomes
thought to be for the most part genetically inactive.
Heteroduplex. A double-stranded DNA molecule or DNA-RNA
hybrid, where each strand is of a different origin.
Heterogeneous nuclear RNA (hnRNA). The name originally given
to large RNA molecules found in the nucleus, which are now
known to be unedited mRNA transcripts, or pre-mRNAs. (See
HGH. See Human growth hormone.
hnRNA. See Heterogeneous nuclear RNA.
Homologous chromosomes. Chromosomes that have the same
linear arrangement of genes--a pair of matching chromosomes
in a diploid organism. See Chromosomes.
Homologous recombination. The exchange of DNA fragments
between two DNA molecules or chromatids of paired
chromosomes (during crossing over) at the site of identical
Homozygote. An organism whose genotype is characterized by
two identical alleles of a gene. See Allele, Genotype.
Host. An organism that contains another organism.
Human Genome Project. A project coordinated by the National
Institutes of Health (NIH) and the Department of Energy
(DOE) to determine the entire nucleotide sequence of the
human chromosomes. (See NIH.)
Human growth hormone (HGH, somatotrophin). A protein
produced in the pituitary gland that stimulates the liver to
produce somatomedins, which stimulate growth of bone and
Hybrid. The offspring of two parents differing in at least
one genetic characteristic (trait). Also, a heteroduplex
DNA or DNA-RNA molecule.
Hybridization. The hydrogen bonding of complementary DNA
and/or RNA sequences to form a duplex molecule. (See
Northern hybridization, Southern hybridization.)
Hybridoma. A hybrid cell, composed of a B Iymphocyte fused
to a tumor cell, which grows indefinitely in tissue culture
and is selected for the secretion of a specific antibody of
Hydrogen bond. A relatively weak bond formed betwee n y. a
hydrogen atom (which is covalently bound to a nitrogen or
oxygen atom) and a nitrogen or oxygen with an unshared
Hydrolysis. A reaction in which a molecule of water is added
at the site of cleavage of a molecule to two products.
Immortalizing oncogene. A gene that upon transfection
enables a primary cell to grow indefinitely in culture.
Incomplete dominance. A condition where a heterozygous off-
spring has a phenotype that is distinctly different from,
and intermediate to, the parental phenotypes. See
Initiation codon. The mRNA sequence AUG, coding for
methionine, which initiates translation of mRNA.
Inositol lipid. A membrane-anchored phospholipid that
transduces hormonal signals by stimulating the release of
any of several chemical messengers. (See Phospholipid.)
Insertion mutations. Changes in the base sequence of a DNA
molecule resulting from the random integration of DNA from
another source. See DNA, Mutation.
In situ. Refers to performing assays or manipulations with
Insulin. A peptide hormone secreted by the islets of
Langerhans of the pancreas that regulates the level of sugar
in the blood.
Interferon. A family of small proteins that stimulate viral
resistance in cells.
Intergenic regions. DNA sequences located between genes that
comprise a large percentage of the human genome with no
Introgression. Backcrossing of hybrids of two plant
populations to introduce new genes into a wild population.
Intron. A noncoding DNA sequence within a gene that is
initially transcribed into messenger RNA but is later
snipped out. See Coding, DNA, Messenger RNA,
Invasiveness. Ability of a plant to spread beyond its
introduction site and become established in new locations
where it may provide a deliterious effect on organisms
already existing there.
In vivo. Refers to biological processes that take place
within a living organism or cell.
Ion. A charged particle.
Isotope. One of two or more forms of an element that have
the same number of protons (atomic number) but differing
numbers of neutrons (mass numbers). Radioactive isotopes are
commonly used to make DNA probes and metabolic tracers.
Joining (J) segment. A small DNA segment that links genes to
yield a functional gene encoding an immunogobulin.
Kanamycin. An antibiotic of the aminoglycoside family that
poisons translation by binding to the ribosomes. See
kanr. Kanamycin resistance gene. (See Selectable marker.)
Karyotype. All of the chromosomes in a cell or an
individual organism, visible through a microsope during cell
Lag phase. The initial growth phase, during which cell
number remains relatively constant prior to rapid growth.
See growth phase.
Lawn. A uniform and uninterrupted laver of bacterial growth,
in which individual colonies cannot be observed.
Legume. A member of the pea family that possesses root
nodules containing nitrogen-fixing bacteria.
Library. A collection of cells, usually bacteria or yeast,
that have been transformed with recombinant vectors carrying
DNA inserts from a single species. (See cDNA library,
Expression library, Genomic library.)
Ligase (DNA ligase). An enzyme that catalyzes a condensation
reaction that links two DNA molecules via the formation of a
phosphodiester bond between the 3' hydroxyl and 5' phosphate
of adjacent nucleotides.
Ligate. The process of joining two or more DNA fragments.
Lineage. A chart that traces the flow of genetic information
from generation to generation.
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.
Linkage map. See Genetic linkage map.
Linked genes/markers. Genes and/or markers that are so
closely associated on the chromosome that they are
coinherited in 80% or more of cases.
Linker. A short, double-stranded oligonucleotide containing
a restriction endonuclease recognition site, which is
ligated to the ends of a DNA fragment.
Liposomes. Membrane-bound vesicles constructed in the
laboratory to transport biological molecules.
Locus (plural = loci). A specific location or site on a
Log phase. See Logarithmic phase.
Logarithmic phase (log or exponential growth phase). The
steepest slope of the growth curve--the phase of vigorous
growth during which cell number doubles every 20-30
minutes. (See Growth phase.)
Lysis. The destruction of the cell membrane.
Lysogen. A bacterial cell whose chromosome contains in-
tegrated viral DNA.
Lysogenic. A type or phase of the virus life cycle during
which the virus integrates into the host chromosome of the
infected cell, often remaining essentially dormant for some
period of time. See Lysogen.
Lytic. A phase of the virus life cycle during which the vi-
rus replicates within the host cell, releasing a new
generation of viruses when the infected cell lyses.
Malignant. Having the properties of cancerous growth.
Mapping. Determining the physical location of a gene or
genetic marker on a chromosome. (See Continuous map,
Genetic map, Physical map.)
Megabase cloning. The cloning of very large DNA fragments.
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
Messenger RNA (mRNA). The class of RNA molecules that copies
the genetic information from DNA, in the nucleus, and
carries it to ribosomes, in the cytoplasm, where it is
translated into protein. (See RNA.)
Metabolism. The biochemical processes that sustain a living
cell or organism.
Metallothionein. A protective protein that binds heavy
metals, such as cadmium and lead.
Microbe. A microorganism.
Microbial mats (biofilms). Layered groups or communities of
Microinjection. A means to introduce a solution of DNA,
protein, or other soluble material into a cell using a fine
Mitosis. The replication of a cell to form two daughter
cells with identical sets of chromosomes.
Molecular biology. The study of the biochemical and mo-
lecular interactions within living cells.
Molecular cloning. The biological amplification of a
specific DNA sequence through mitotic division of a host
cell into which it has been transformed or transfected.
Molecular genetics. The study of the flow and regulation of
genetic information between DNA, RNA, and protein molecules.
Monoclonal antibodies. Immunoglobulin molecules of single-
epitope specificity that are secreted by a clone of B cells.
Monoculture. The agricultural practice of cultivating crops
consisting of genetically similar organisms.
Monogenic. Controlled by or associated with a single gene.
Movable genetic element. (See Transposon.)
mRNA. See Messenger RNA.
Multi-locus probe. A probe that hybridizes to a number of
different sites in the genome of an organism. (See Probe.)
Mutagen. Any agent or process that can cause mutations.
Mutation. An alteration in DNA structure or sequence of a
gene. (See Point mutation.)
Mutualism. See Symbiosis.
Mycorrhizae. Fungi that form symbiotic relationships with
roots of more developed plants.
National Institutions of Health (NIH). A nonregulatory
agency which has oversight of research activities that the
National Science Foundation (NSF). A nonregulatory agency
which has oversight of biotechnology research activities
that the agency funds.
Natural selection. The differential survival and reproduc-
tion of organisms with genetic characteristics that enable
them to better utilize environmental resources.
Nick translation. A procedure for making a DNA probe in
which a DNA fragment is treated with DNase to produce
single-stranded nicks, followed by incorporation of
radioactive nucleotides from the nicked sites by DNA
Nicked circle (relaxed circle). During extraction of plasmid
DNA from the bacterial cell, one strand of the DNA becomes
nicked. This relaxes the torsional strain needed to maintain
supercoiling, producing the familiar form of plasmid. (See
NIH. See National Institutes of Health.
Nitrocellulose. A membrane used to immobilize DNA, RNA, or
protein, which can then be probed with a labeled sequence or
Nitrogen fixation. The conversion of atmospheric nitrogen to
biologically usable nitrates.
Nitrogenous bases. The purines (adenine and guanine) and
pyrimidines (thymine, cytosine, and uracil) that comprise
DNA and RNA molecules.
Nodule. The enlargement or swelling on roots of nitrogen-
fixing plants. The nodules contain symbiotic nitrogen-
fixing bacteria. See Nitrogen fixation.
Nontarget organism. An organism which is affected by an
interaction for which it was not the intended recipient.
Northern blotting. See Northern hybridization.
Northern hybridization. (Northern blotting). A procedure in
which RNA fragments are transferred from an agarose gel to a
nitrocellulose filter, where the RNA is then hybridized to a
radioactive probe. (See Hybridization.)
NSF. See National Science Foundation.
Nuclease. A class of enzymes that degrades DNA and/or RNA
molecules by cleaving the phosphodiester bonds that link
adjacent nucleotides. In deoxyribonuclease (DNase), the
substrate is DNA. In endonuclease, it cleaves at internal
sites in the substrate molecule. Exonuclease progressively
cleaves from the end of the substrate molecule. In
ribonuclease (RNase), the substrate is RNA. In the S1
nuclease, the substrate is single-stranded DNA or RNA.
Nucleic acids. The two nucleic acids, deoxyribonucleic acid
(DNA) and ribonucleic acid (RNA), are made up of long chains
of molecules called nucleotides. See DNA, RNA, Nucleotides.
Nuclein. The term used by Friedrich Miescher to describe the
nuclear material he discovered in 1869, which today is known
Nucleoside. A building block of DNA and RNA, consisting of a
nitrogenous base linked to a five carbon sugar. (See
Nucleoside analog. A synthetic molecule that resembles a
naturally occuring nucleoside, but that lacks a bond site
needed to link it to an adjacent nucleotide. (See
Nucleotide. A building block of DNA and RNA, consisting of a
nitrogenous base, a five-carbon sugar, and a phosphate
group. Together, the nucleotides form codons, which when
strung together form genes, which in turn link to form
chromosomes. (See Chromosome, Codon, Complementary
nucleotides, Dideoxynucleotide, DNA, Gene, Oligonucleotide,
Nucleus. The membrane-bound region of a eukaryotic cell that
contains the chromosomes.
Occupational Safety and Health Act. See Occupational Safety
and Health Administration.
Occupational Safety and Health Administration (OSHA). One
of the U.S. agencies responsible for regulation of
biotechnology. The major law under which the agency has
regulatory powers is the Occupational Safety and Health Act.
Oligonucleotide. A DNA polymer composed of only a few
nucleotides. (See Nucleotide.)
Oncogene. A gene that contributes to cancer formation when
mutated or inappropriately expressed. (See Cellular
oncogene, Dominant oncogene, Immortalizing oncogene,
Oncogenesis. The progression of cytological, genetic, and
cellular changes that culminate in a malignant tumor.
Open pollination. Pollination by wind, insects, or other
Open reading frame. A long DNA sequence that is unin-
terrupted by a stop codon and encodes part or all of a
protein. (See Reading frame.)
Operator. A prokaryotic regulatory element that interacts
with a repressor to control the transcription of adjacent
Organelle. A cell structure that carries out a specialized
function in the life of a cell.
Origin of replication. The nucleotide sequence at which DNA
synthesis is initiated.
OSHA. See Occupational Safety and Health Administration.
Overlapping reading frames. Start codons in different
reading frames generate different polypeptides from the same
DNA sequence. (See Reading frame.)
Ovum. A female gamete.
Paleontology. The study of the fossil record of past geo-
logical periods and of the phylogenetic relationships
between ancient and contemporary plant and animal species.
Palindrome. See Palindromic sequence.
Palindromic sequence. A DNA locus whose 5'-to-3' sequence is
identical on each DNA strand. The sequence is the same when
one strand is read left to right and the other strand is
read right to left. Recognition sites of many restriction
enzymes are palindromic. See DNA.
pAMP. Ampicillin-resistant plasmid developed for this
laboratory course. (See Plasmid.)
Parasitism. The closee association of two or more
dissimilar organisms where the association is harmful to at
least one. See Commensalism, Parasitism, Symbiosis.
Pathogen. Organism which can cause disease in another
pBR322. A derivation of ColE1, one of the first plasmid
vectors widely used. (See Plasmid.)
PCR. See Polymerase chain reaction.
Pedigree. A diagram mapping the genetic history of a par-
Persistence. Ability of an organism to remain in a
particular setting for a period of time after it is
Pesticide. A substance that kills harmful organisms (for
example, an insecticide or fungicide).
Phage (particle). See Bacteriophage.
Phenotype. The observable characteristics of an organism,
the expression of gene alleles (genotype) as an observable
physical or biochemical trait. See Genotype.
Pheromone. A hormone-like substance that is secreted into
Phosphatase. An enzyme that hydrolyzes esters of phosphoric
acid, removing a phosphate group.
Phosphodiester bond. A bond in which a phosphate group joins
adjacent carbons through ester linkages. A condensation
reaction between adjacent nucleotides results in a
phosphodiester bond between 3' and 5' carbons in DNA and
Phospholipid. A class of lipid molecules in which a phos-
phate group is linked to glycerol and two fatty acyl groups.
A chief component of biological membranes. (See Inositol
Phosphorylation. The addition of a phosphate group to a
Physical map. A map showing physical locations on a DNA
molecule, such as restriction sites, and sequence-tagged
sites. (See Mapping.)
Plant Pest Act (PPA). See U.S. Department of Agriculture.
Plant Variety Act (PVA). See U.S. Department of
Plaque. A clear spot on a lawn of bacteria or cultured cells
where cells have been Iysed by viral infection.
Plasmid (p). A circular DNA molecule, capable of autonomous
replication, which typically carries one or more genes
encoding antibiotic resistance proteins. Plasmids can
transfer genes between bacteria and are important tools of
transformation for genetic engineers. (See Nicked circle,
pAMP, Relaxed plasmid, Stringent plasmid, Supercoiled
Pleiotrophy. The effect of a particular gene on several
Point mutation. A change in a single base pair of a DNA
sequence in a gene. (See Mutation.)
Poly(A) polymerase. Catalyzes the addition of adenine
residues to the 3' end of pre-mRNAs to form the poly(A)
tail. (See Polymerase.)
Polyacrylamide gel electrophoresis. Electrophoresis
through a matrix composed of a synthetic polymer, used to
separate proteins, small DNA, or RNA molecules of up to 1000
nucleotides. Used in DNA sequencing. (See Electrophoresis.)
Polyclonal antibodies. A mixture of immunoglobulin
molecules secreted against a specific antigen, each
recognizing a different epitope.
Polygenic. Controlled by or associated with more than one
Polylinker. A short DNA sequence containing several re-
striction enzyme recognition sites that is contained in
Polymer. A molecule composed of repeated subunits.
Polymerase (DNA). Synthesizes a double-stranded DNA
molecule using a primer and DNA as a template. (See Poly(A)
polymerase, Polymerase chain reaction, RNA polymerase, Taq
Polymorphisms. Variant forms of a particular gene that
occur simultaneously in a population.
Polynucleotide. A DNA polymer composed of multiple
nucleotides. (See Nucleotide.)
polymerase chain reaction (PCR). A procedure that en-
zymatically amplifies a DNA polymerase. (See Polymerase.)
Polypeptide (protein). A polymer composed of multiple amino
acid units linked by peptide bonds.
Polyploid. A multiple of the haploid chromosome number that
results from chromosome replication without nuclear
Polysaccharide. A polymer composed of multiple units of
monosaccharide (simple sugar).
Polyvalent vaccine. A recombinant organism into which has
been cloned antigenic determinants from a number of
different disease-causing organisms. (See Vaccine.)
Population. A local group of organisms belonging to the
same species and capable of interbreeding.
PPA. See U.S. Department of Agriculture.
Prion. See Proteinaceous infectious particle.
Probe. A sequence of DNA or RNA, labeled or marked with a
radioactive isotope, used to detect the presence of
complementary nucleotide sequences. See Nucleotide.
Prokaryote. A bacterial cell lacking a true nucleus; its
DNA is usually in one long strand. See Eukaryote.
Proto-oncogene. See oncogene.
Primary cell. A cell or cell line taken directly from a
living organism, which is not immortalized.
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.
Probe. A single-stranded DNA that has been radioactively
labeled and is used to identify complementary sequences in
genes or DNA fragments of interest. (See Multilocus probe.)
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. (See
Pronucleus. Either of the two haploid gamete nuclei just
prior to their fusion in the fertilized ovum.
Protease. An enzyme that cleaves peptide bonds that link
amino acids in protein molecules.
Protein. A polymer of amino acids linked via peptide bonds
and which may be composed of two or more polypeptide chains.
Proteinaceous infectious particle (prion). A proposed
pathogen composed only of protein with no detectable nucleic
acid and which is responsible for Creutzfeldt-Jakob disease
and kuru in humans and scrapie in sheep.
Protein kinase. An enzyme that adds phosphate groups to a
protein molecule at serine, threonine, or tyrosine residues.
Proteolytic. The ability to break down protein molecules.
Provirus. See virus.
Public Health Service Act. See Food and Drug
pUC. A widely used expression plasmid containing a
-galactosidase gene. (See Plasmid.)
PVA. The Plant Variety Act. See U.S. Department of
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. (See Open
reading frame, Overlapping reading frames.)
Recessive(-acting) oncogene, (anti-oncogene). A single copy
of this gene is sufficient to suppress cell proliferation;
the loss of both copies of the gene contributes to cancer
formation. (See Oncogene.)
Recessive gene. Characterized as having a phenotype
expressed only when both copies of the gene are mutated or
Recognition sequence (site). A nucleotide sequence--composed
typically of 4, 6, or 8 nucleotides--that is recognized by a
restriction endonuclease. Type II enzyrnes cut (and their
corresponding modification enzymes methylate) within or very
near the recognition sequence.
Recombinant. A cell that results from recombination of
Recombinant DNA. The process of cutting and recombining DNA
fragments from different sources as a means to isolate genes
or to alter their structure and function.
Recombination frequency. The frequency at which crossing
over occurs between two chromosomal loci--the probability
that two loci will become unlinked during meiosis.
Regulatory gene. A gene whose protein controls the activity
of other genes or metabolic pathways.
Relaxed circle plasmid. See Plasmid.
Relaxed plasmid. A plasmid that replicates independently of
the main bacterial chromosome and is present in 10-500
copies per cell. (See Plasmid.)
Renature. The reannealing (hydrogen bonding) of single-
stranded DNA and/or RNA to form a duplex molecule.
Replicon. A chromosomal region containing the DNA sequences
necessary to initiate DNA replication processes.
Repressor. A DNA-binding protein in prokaryotes that blocks
gene transcription by binding to the operator.
Restriction endonuclease (enzyme). A class of endonucleases
that cleaves DNA after recognizing a specific sequence, such
as BamH1 (GGATCC), EcoRI (GAATTC), and HindIII (AAGCTT).
Type I. Cuts nonspecifically a distance greater than 1000
bp from its recognition sequence and contains both
restriction and methylation activities.
Type II. Cuts at or near a short, and often symmetrical,
recognition sequence. A separate enzyme methylates the same
Type III. Cuts 24-26 bp downstream from a short,
asymmetrical recognition sequence. Requires ATP and contains
both restriction and methylation activities.
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.
Restriction map. See Mapping.
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 hostcell
chromosome. Many naturally occurring cancers of vertebrate
animals are caused by retroviruses.
Reverse genetics. Using linkage analysis and polymorphic
markers to isolate a disease gene in the absence of a known
metabolic defect, then using the DNA sequence of the cloned
gene to predict the amino acid sequence of its encoded
Reverse transcriptase (RNA-dependent DNA polymerase). An
enzyme isolated from retrovirus-infected cells that
synthesizes a complementary (c)DNA strand from an RNA
RFLP. See Restriction-fragment-length polymorphism.
Rhizobia. Bacteria in a symbiotic relationship with
leguminous plants that results in nitrogen fixation. See
Rhizosphere. The soils region on and around plant roots.
Ribozyme. See Catalytic RNA.
Ribosomal RNA (rRNA). The RNA component of the ribosome.
Ribosome. Cellular organelle that is the site of protein
synthesis during translation. See Organelle, Translation.
Ribosome-binding site. The region of an mRNA molecule that
binds the ribosome to initiate translation.
RNA (ribonucleic acid). An organic acid composed of re-
peating nucleotide units of adenine, guanine, cytosine, and
uracil, whose ribose components are linked by phosphodiester
bonds. (See Antisense RNA, Heterogeneous nuclear RNA,
Messenger RNA, Ribosomal RNA, RNA polymerase, Small nuclear
RNA, Transfer RNA.)
RNA polymerase. Transcribes RNA from a DNA template. (See
rRNA. See Ribosomal RNA.
Salmonella. A genus of rod-shaped, gram-negative bacteria
that are a common cause of food poisoning.
Satellite RNA (viroids). A small, self-splicing RNA molecule
that accompanies several plant viruses, including tobacco
S&E. See U.S. Department of Agriculture.
Self-pollination. Pollen of one plant is transferred to the
female part of the same plant or another plant with the same
Selectable marker. A gene whose expression allows one to
identify cells that have been transforrned or transfected
with a vector containing the marker gene. (See B-Lactamase,
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
Sequence hypothesis. Francis Crick's seminal concept that
genetic information exists as a linear DNA code; DNA and
protein sequence are colinear.
Sequence-tagged site (STS). A unique (single-copy) DNA
sequence used as a mapping landmark on a chromosome.
Sexual reproduction. The process where two cells (gametes)
fuse to form one hybrid, fertilized cell. See Asexual
reproduction, Gamete, Hybrid.
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, pro-
teins, and messengers.
Site-directed mutagenesis. The process of introducing spe-
cific base-pair mutations into a gene.
Small nuclear RNA (snRNA). Short RNA transcripts of 100-300
bp that associate with proteins to form small nuclear
ribonucleoprotein particles (snRNPs), which participate in
RNA processing. (See RNA.)
snRNA. See Small nuclear RNA.
Somatic cell. Any nongerm cell that composes the body of an
organism and which possesses a set of multiploid chromosomes
(diploid in most organisms). (See Gamete, Somatic cell gene
Somatic cell gene therapy. The repair or replacement of a
defective gene within somatic tissue. (See Somatic cell.)
Somatotrophin. See Human growth hormone.
Southern blotting. See Southern hybridization.
Southern hybridization (Southern blotting). A procedure in
which DNA restriction fragments are transferred from an
agarose gel to a nitrocellulose filter, where the denatured
DNA is then hybridized to a radioactive probe (blotting).
Species. A classification of related organisms that can
Spore. A form taken by certain microbes that enables them to
exist in a dormant stage. It is an asexual reproductive
cell. See Asexual reproduction, Dormant.
Stationary phase. The plateau of the growth curve after log
growth, during which cell number remains constant. New cells
are produced at the same rate as older cells die. (See
Sticky end. A protruding, single-stranded nucleotide se-
quence produced when a restriction endonuclease cleaves off
center in its recognition sequence.
Stringency. Reaction conditions--notably temperature, salt,
and pH--that dictate the annealing of single-stranded
DNA/DNA, DNA/RNA, and RNA/RNA hybrids. At high stringency,
duplexes form only between strands with perfect one-to-one
complementarity; lower stringency allows annealing between
strands with some degree of mismatch between bases.
Stringent plasmid. A plasmid that only replicates along with
the main bacterial chromosome and is present as a single
copy, or at most several copies, per cell. (See plasmid.)
STS. See Sequence-tagged site.
Stop codon. See Termination codon.
Structure-functionalism. The scientific tradition that
stresses the relationship between a physical structure and
its function, for example, the related disciplines of
anatomy and physiology.
Subcloning. The process of tranferring a cloned DNA fragment
from one vector to another. (See Cloning.)
Subunit vaccine. A vaccine composed of a purified antigenic
determinant that is separated from the virulent
organism. (See Vaccine, Enzyme.)
Supercoiled plasmid. The predominant in vivo form of
plasmid, in which the plasmid is coiled around histone-like
proteins. Supporting proteins are stripped away during
extraction from the bacterial cell, causing the plasmid
molecule to supercoil around itself in vitro. (See
Supergene. A group of neighboring genes on a chromosome
that tend to be inherited together and sometimes are
Supernatant. The soluble liquid &action of a sample after
centrifugation or precipitation of insoluble solids.
Symbiosis. The close association of two or more dissimilar
organisms where both receive an advantage from the
association. See Commensalism, Parasitism.
Synapsis. The pairing of homologous chromosome pairs during
prophase of the first meiotic division, when crossing over
Taq polymerase. A heat-stable DNA polymerase isolated from
the bacterium Therrnus aquaticus, used in PCR. (See
TATA box. An adenine- and thymine-rich promoter sequence
located 25-30 bp upstream of a gene, which is the binding
site of RNA polymerase.
T-DNA (transfer DNA, tumor-DNA). The transforming region of
DNA in the Ti plasmid of Agrobacterium tumefaciens.
Telomere. The end of a chromosome.
Template. An RNA or single-stranded DNA molecule upon which
a complementary nucleotide strand is synthesized.
Termination 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. Also known as stop codon. (See
Terminator region. A DNA sequence that signals the end of
Tetracycline. An antibiotic that interferes with protein
synthesis in prokaryotes.
Thymidine kinase (tk). An enzyme that allows a cell to
utilize an alternate metabolic pathway for incorporating
thymidine into DNA. Used as a selectable marker to identify
transfected eukaryotic cells.
Ti (tumor-inducing) plasmid. A giant plasmid of Agrobac-
terium tumefaciens that is responsible for tumor formation
in infected plants. Ti plasmids are used as vectors to
introduce foreign DNA into plant cells.
Toxic Substances Control Act (TSCA). See Environmental
Trait. See Phenotype.
Transcapsidation. The partial of full coating of the
nucleic acid of one virus with a coat protein of a differing
virus. See Coat protein.
Transcription. The process of creating a complementary RNA
copy of DNA.
Transducing phage. See Transduction.
Transduction. The transfer of DNA sequences from one
bacterium to another via lysogenic infection by a
bacteriophage (transducing phage).
Transfection. The uptake and expression of a foreign DNA
sequence by cultured eukaryotic cells.
Transfer DNA. See T-DNA.
Transfer RNA (tRNA). See tRNA.
Transformant. In prokaryotes, a cell that has been ge-
netically altered through the uptake of foreign DNA. In
higher eukaryotes, a cultured cell that has acquired a
malignant phenotype. (See Transformation.)
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. (See Transformant,
Transformation efficiency. The number of bacterial cells
that uptake and express plasmid DNA divided by the mass of
plasmid used (in transformants/microgram). (See
Transforming oncogene. A gene that upon transfection
converts a previously immortalized cell to the malignant
phenotype. (See Oncogene.)
Transgene. See Transgenic.
Transgenic. An organism in which a foreign DNA gene (a
transgene) is incorporated into its genome early in de-
velopment. 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. See Transgenic animal,
Transgenic animal. Genetically enginnered animal or
offspring of genetically engineered animals. The transgenic
animal usually contains material from at lease one unrelated
organism, such as from a virus, plant, or other animal. See
Transgenic plant. Genetically engineered plant or offspring
of genetically engineered plants. The transgenic plant
usually contains material from at least one unrelated
organisms, such as from a virus, animal, or other plant.
Transition-state intermediate. In a chemical reaction, an
unstable and high-energy configuration assumed by reactants
on the way to making products. Enzymes are thought to bind
and stabilize the transition state, thus lowering the energy
of activation needed to drive the reaction to completion.
Translation. The process of converting the genetic infor-
mation of an mRNA on ribosomes into a polypeptide. Transfer
RNA molecules carry the appropriate amino acids to the
ribosome, where they are joined by peptide bonds.
Translocation. The movement or reciprocal exchange of
large-chromosomal segments, typically between two different
Transposable genetic element. See Transposon.
Transposition. The movement of a DNA segment within the
genome of an organism.
Transposon (transposable, or movable genetic element). A
relatively small DNA segment that has the ability to move
from one chromosomal position to another.
tRNA (transfer RNA). The class of small RNA molecules that
transfer amino acids to the ribosome during protein
synthesis. See Transfer RNA.
Trypsin. A proteolytic enzyme that hydrolyzes peptide bonds
on the carboxyl side of the amino acids arginine and lysine.
TSCA. The Toxic Substances Control Act. See
Environmental Protection Agency.
Tumor DNA. See T-DNA.
Tumor-inducing plasmid. See Ti plasmid.
Tumor virus. A virus capable of transforming a cell to a
malignant phenotype. (See Virus.)
Upstream. The region extending in a 5' direction from a
USDA. See The U.S. Department of Agriculture.
U.S. Department of Agriculture. The U.S. agency responsible
for regulation of biotechnology products in plants and
animals. The major laws under which the agency has
regulatory powers include the Federal Plant Pest Act (PPA),
the Federal Seed Act, and the Plant Variety Act (PVA). In
addition, the Science and Education (S&E) division has
nonregulatory oversight of research activities that the
Vaccine. A preparation of dead or weakened pathogen, or of
derived antigenic determinants, that is used to induce
formation of antibodies or immunity against the pathogen.
(See Polyvalent vaccine, Subunit vaccine.)
Vaccinia. The cowpox virus used to vaccinate against
smallpox and, experimentally, as a carrier of genes for
antigenic determinants cloned from other disease organisms.
Variable surface glycoprotein (VSG). One of a battery of
antigenic determinants expressed by a microorganism to elude
Variation. Differences in the frequency of genes and traits
among individual organisms within a population.
Vector. An autonomously replicating DNA molecule into which
foreign DNA fragments are inserted and then propagated in a
host cell. Also living carriers of genetic material (such
as pollen) from plant to plant, such as insects.
Viral oncogene. A viral gene that contributes to malig-
nancies in vertebrate hosts.
Viroid. A plant pathogen that consists of a naked RNA
molecule of approximately 250-350 nucleotides, whose
extensive base pairing results in a nearly correct double
helix. (See Satellite RNA.)
Virulence. The degree of ability of an organism to cause
Virus. An infectious particle composed of a protein capsule
and a nucleic acid core, which is dependent on a host
organism for replication. A double-stranded DNA copy of an
RNA virus genome that is integrated into the host chromosome
during lysogenic infection. (See Coat protein, DNA, Genome,
Host, Nucleic acid, RNA, Tumor virus.)
VSG. See Variable surface glycoprotein.
Weed. An undesirable plant.
Weediness. Unwanted effects of a plant.
Wild type. An organism as found in nature; the organism
before it is genetically engineered.
X-linked disease. A genetic disease caused by a mutation on
the X chromosome. In X-linked recessive conditions, a normal
female "carrier" passes on the mutated X chromosome to an
X-ray crystallography. The diffraction pattern of X-rays
passing through a pure crystal of a substance.
Z-DNA. A region of DNA that is "flipped" into a lefthanded
helix, characterized by alternating purines and pyrimidines,
and which may be the target of a DNA-binding protein.
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