最新基因组学术语表New Genome Glossary

最新基因组学术语表New Genome Glossary
Genome Glossary

A
Adenine (A): A nitrogenous base, one member of the base pair AT
(adeninethymine).

Allele: Alternative form of a genetic locus; a single allele for each locus is
inherited separately from each parent (e.g., at a locus for eye color the allele
might result in blue or brown eyes).

Amino acid: Any of a class of 20 molecules that are combined to form
proteins in living things. The sequence of amino acids in a protein and hence
protein function are determined by the genetic code.

Amplification: An increase in the number of copies of a specific DNA
fragment; can be in vivo or in vitro. See cloning, polymerase chain reaction .
Arrayed library: Individual primary recombinant clones (hosted in phage,
cosmid, YAC, or other vector) that are placed in two-dimensional arrays in
microtiter dishes. Each primary clone can be identified by the identity of the
plate and the clone location (row and column) on that plate. Arrayed libraries
of clones can be used for many applications, including screening for a
specific gene or genomic region of interest as well as for physical mapping.
Information gathered on individual clones from various genetic linkage and
physical map analyses is entered into a relational database and used to
construct physical and genetic linkage maps simultaneously; clone identifiers
serve to interrelate the multilevel maps. Compare library, genomic library.

Autoradiography: A technique that uses X-ray film to visualize
radioactively labeled molecules or fragments of molecules; used in analyzing
length and number of DNA fragments after they are separated by gel
electrophoresis.

Autosome: A chromosome not involved in sex determination. The diploid
human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1
pair of sex chromosomes (the X and Y chromosomes).

B
BAC: See bacterial artificial chromosome.
Bacterial artificial chromosome (BAC): A vector used to clone DNA
fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli
cells. Based on naturally occurring F-factor plasmid found in the bacterium E.
coli. Compare cloning vector .
Bacteriophage: See phage.
Base pair (bp): Two nitrogenous bases (adenine and thymine or guanine
and cytosine) held together by weak bonds. Two strands of DNA are held
together in the shape of a double helix by the bonds between base pairs.
Base sequence: The order of nucleotide bases in a DNA molecule.
Base sequence analysis: A method, sometimes automated, for
determining the base sequence.
Biotechnology: A set of biological techniques developed through basic
research and now applied to research and product development. In
particular, the use by industry of recombinant DNA, cell fusion, and new
bioprocessing techniques.
bp: See base pair .

C
cDNA: See complementary DNA.
Centimorgan (cM): A unit of measure of recombination frequency. One
centimorgan is equal to a 1% chance that a marker at one genetic locus will
be separated from a marker at a second locus due to crossing over in a
single generation. In human beings, one centimorgan is equivalent, on
average, to one million base pairs.
Centromere: A specialized chromosome region to which spindle fibers
attach during cell division.
Chromosome: The self -replicating genetic structure of cells containing the
cellular DNA that bears in its nucleotide sequence the linear array of genes.
In prokaryotes, chromosomal DNA is circular, and the entire genome is
carried on one chromosome. Eukaryotic genomes consist of a number of
chromosomes whose DNA is associated with different kinds of proteins.
Clone bank: See genomic library.
Clone: An exact copy made of biological material such as a DNA segment (a
gene or other region), a whole cell, or a complete organism.
Cloning: Using specialized DNA technology (see cloning vector ) to produce
multiple, exact copies of a single gene or other segment of DNA to obtain
enough material for further study. This process is used by researchers in the
Human Genome Project, and is referred to as cloning DNA.?The resulting
cloned (copied) collections of DNA molecules are called clone libraries. A
second type of cloning exploits the natural process of cell division to make
many copies of an entire cell. The genetic makeup of these cloned cells,
called a cell line, is identical to the original cell. A third type of cloning
produces complete, genetically identical animals such as the famous Scottish
sheep, Dolly.?
Cloning vector: DNA molecule originating from a virus, a plasmid, or the
cell of a higher organism into which another DNA fragment of appropriate
size can be integrated without loss of the vectors capacity for selfreplication;
vectors introduce foreign DNA into host cells, where it can be reproduced in
large quantities. Examples are plasmids, cosmids, and yeast artificial
chromosomes; vectors are often recombinant molecules containing DNA
sequences from several sources.
cM: See centimorgan.
Code: See genetic code .
Codon: See genetic code
Complementary DNA (cDNA): DNA that is synthesized from a messenger
RNA template; the single-stranded form is often used as a probe in physical
mapping.
Complementary sequence: Nucleic acid base sequence that can form a
doublestranded structure by matching base pairs with another sequence; the
complementary sequence to GTAC is CATG.
Conserved sequence: A base sequence in a DNA molecule (or an amino
acid sequence in a protein) that has remained essentially unchanged
throughout evolution.
Contig: Group of cloned (copied) pieces of DNA representing overlapping
regions of a particular chromosome.
Contig map: A map depicting the relative order of a linked library of small
overlapping clones representing a complete chromosomal segment.
Cosmid: Artificially constructed cloning vector containing the cos gene of
phage lambda. Cosmids can be packaged in lambda phage particles for
infection into E. coli; this permits cloning of larger DNA fragments (up to
45kb) than can be introduced into bacterial hosts in plasmid vectors.
Crossing over: The breaking during meiosis of one maternal and one
paternal chromosome, the exchange of corresponding sections of DNA, and
the rejoining of the chromosomes. This process can result in an exchange of
alleles between chromosomes. Compare recombination.
Cytosine (C): A nitrogenous base, one member of the base pair GC
(guanine and cytosine).
D Deletion Map: A description of a specific chromosome that uses defined
mutations -specific deleted areas in the genome- as "biochemical signposts,"
or markers for specific areas.
Deoxyribonucleotide: See nucleotide .
Diploid: A full set of genetic material, consisting of paired chromosomes one
chromosome from each parental set. Most animal cells except the gametes
have a diploid set of chromosomes. The diploid human genome has 46
chromosomes. Compare haploid.
DNA (deoxyribonucleic acid): The molecule that encodes genetic
information. DNA is a doublestranded molecule held together by weak bonds
between base pairs of nucleotides. The four nucleotides in DNA contain the
bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature,
base pairs form only between A and T and between G and C; thus the base
sequence of each single strand can be deduced from that of its partner.
DNA probe: See probe.
DNA replication: The use of existing DNA as a template for the synthesis
of new DNA strands. In humans and other eukaryotes, replication occurs in
the cell nucleus.
DNA sequence: The relative order of base pairs, whether in a fragment of
DNA, a gene, a chromosome, or an entire genome. See base sequence
analysis.
Domain: A discrete portion of a protein with its own function. The
combination of domains in a single protein determines its overall function.
Double helix: The shape that two linear strands of DNA assume when
bonded together.

E
E. coli: Common bacterium that has been studied intensively by geneticists
because of its small genome size, normal lack of pathogenicity, and ease of
growth in the laboratory.
Electrophoresis: A method of separating large molecules (such as DNA
fragments or proteins) from a mixture of similar molecules. An electric
current is passed through a medium containing the mixture, and each kind of
molecule travels through the medium at a different rate, depending on its
electrical charge and size. Separation is based on these differences. Agarose
and acrylamide gels are the media commonly used for electrophoresis of
proteins and nucleic acids.
Endonuclease: An enzyme that cleaves its nucleic acid substrate at internal
sites in the nucleotide sequence.
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.
EST: Expressed sequence tag. See sequence tagged site.
Eukaryote: Cell or organism with membranebound, structurally discrete
nucleus and other welldeveloped subcellular compartments. Eukaryotes
include all organisms except viruses, bacteria, and bluegreen algae. Compare
prokaryote. See chromosome.
Evolutionarily conserved: See conserved sequence.
Exogenous DNA: DNA originating outside an organism.
Exon: The proteincoding DNA sequence of a gene. Compare intron.
Exonuclease: An enzyme that cleaves nucleotides sequentially from free
ends of a linear nucleic acid substrate.
Expressed gene: See gene expression.

F
FISH (fluorescence in situ hybridization): A physical mapping approach
that uses fluorescein tags to detect hybridization of probes with metaphase
chromosomes and with the lesscondensed somatic interphase chromatin.
Flow cytometry: Analysis of biological material by detection of the
lightabsorbing or fluorescing properties of cells or subcellular fractions (i.e.,
chromosomes) passing in a narrow stream through a laser beam. An
absorbance or fluorescence profile of the sample is produced. Automated
sorting devices, used to fractionate samples, sort successive droplets of the
analyzed stream into different fractions depending on the fluorescence
emitted by each droplet.
Flow karyotyping: Use of flow cytometry to analyze and separate
chromosomes on the basis of their DNA content.

G
Gamete: Mature male or female reproductive cell (sperm or ovum) with a
haploid set of chromosomes (23 for humans).
Gel Electrophoresis: a DNA separation technique that is very important in
DNA sequencing. Standard sequencing procedures involve cloning DNA
fragments into special sequencing cloning vectors that carry tiny pieces of
DNA. The next step is to determine the base sequence of the tiny fragments
by a special procedure that generates a series of even tinier DNA fragments
that differ in size by only one base. These nested fragments are separated
by gel electrophoresis, in which the DNA pieces are added to a gelatinous
solution, allowing the fragments to work their way down through the gel.
Smaller pieces move faster and will reach the bottom first. Movement
through the gel is hastened by applying an electrical field to the gel.
Gene: The fundamental physical and functional unit of heredity. A gene is
an ordered sequence of nucleotides located in a particular position on a
particular chromosome that encodes a specific functional product (i.e., a
protein or RNA molecule). See gene expression.
Gene expression: The process by which a gene's coded information is
converted into the structures present and operating in the cell. Expressed
genes include those that are transcribed into mRNA and then translated into
protein and those that are transcribed into RNA but not translated into
protein (e.g., transfer and ribosomal RNAs).
Gene family: Group of closely related genes that make similar products.
Gene library: See genomic library.
Gene mapping: Determination of the relative positions of genes on a DNA
molecule (chromosome or plasmid) and of the distance, in linkage units or
physical units, between them.
Gene product: The biochemical material, either RNA or protein, resulting
from expression of a gene. The amount of gene product is used to measure
how active a gene is; abnormal amounts can be correlated with
diseasecausing alleles.
Genetic code: The sequence of nucleotides, coded in triplets (codons)
along the mRNA, that determines the sequence of amino acids in protein
synthesis. The DNA sequence of a gene can be used to predict the mRNA
sequence, and the genetic code can in turn be used to predict the amino
acid sequence.
Genetic engineering technology: See recombinant DNA technology.
Genetic map: See linkage map.
Genetic material: See genome.
Genetics: The study of the patterns of inheritance of specific traits.
Genome: All the genetic material in the chromosomes of a particular
organism; its size is generally given as its total number of base pairs.
Genome project: Research and technology development effort aimed at
mapping and sequencing some or all of the genome of human beings and
other organisms.
Genomic library: A collection of clones made from a set of randomly
generated overlapping DNA fragments representing the entire genome of an
organism. Compare library, arrayed library.
Genomic sequence: The order of the subunits, called bases, that make up
a particular fragment of DNA in a genome.?DNA is a long molecule made up
of?four different kinds of bases, which are abbreviated A, C, T, and G.?A
DNA fragment that is 10 bases long might have a base sequence of, for
example, ATCGTTCCTG. The particular sequence of bases encodes important
information in an individual's genetic blueprint, and is unique for each
individual (except identical twins).
Guanine (G): A nitrogenous base, one member of the base pair GC
(guanine and cytosine).

H
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 reproductive cells.
Compare diploid.

Heterozygosity: The presence of different alleles at one or more loci on
homologous chromosomes.

Homeobox: A short stretch of nucleotides whose base sequence is virtually
identical in all the genes that contain it. It has been found in many
organisms from fruit flies to human beings. In the fruit fly, a homeobox
appears to determine when particular groups of genes are expressed during
development.

Homology: Similarity in DNA or protein sequences between individuals of
the same species or among different species.

Homologous chromosome: Chromosome containing the same linear gene
sequences as another, each derived from one parent.

Human gene therapy: Insertion of normal DNA directly into cells to correct
a genetic defect.

Human Genome Initiative: Collective name for several projects begun in
1986 by DOE to (1) create an ordered set of DNA segments from known
chromosomal locations, (2) develop new computational methods for
analyzing genetic map and DNA sequence data, and (3) develop new
techniques and instruments for detecting and analyzing DNA. This DOE
initiative is now known as the Human Genome Program. The national effort,
led by DOE and NIH, is known as the Human Genome Project.
Hybridization: The process of joining two complementary strands of DNA
or one each of DNA and RNA to form a double-stranded molecule.
I Informatics: The study of the application of computer and statistical
techniques to the management of information. In genome projects,
informatics includes the development of methods to search databases
quickly, to analyze DNA sequence information, and to predict protein
sequence and structure from DNA sequence data.
In situ hybridization: Use of a DNA or RNA probe to detect the presence
of the complementary DNA sequence in cloned bacterial or cultured
eukaryotic cells.
Interphase: The period in the cell cycle when DNA is replicated in the
nucleus; followed by mitosis.
Intron: The DNA base sequence interrupting the protein coding sequence of
a gene; this sequence is transcribed into RNA but is cut out of the message
before it is translated into protein. Compare exon.
In vitro: Outside a living organism.

K
Karyotype: A photomicrograph of an individual's chromosomes arranged in
a standard format showing the number, size, and shape of each
chromosome type; used in low-resolution physical mapping to correlate
chromosomal abnormalities with the characteristics of specific diseases.
kb: See kilobase.
Kilobase (kb): Unit of length for DNA fragments equal to 1000
nucleotides.

L
Library: An unordered collection of clones (i.e., cloned DNA from a
particular organism), whose relationship to each other can be established by
physical mapping. Compare genomic library, arrayed library.
Linkage: The proximity of two or more markers (e.g., genes, RFLP markers)
on a chromosome; the closer together the markers are, the lower the
probability that they will be separated during DNA repair or replication
processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes),
and hence the greater the probability that they will be inherited together.
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. Distance is measured in centimorgans (cM).
Localize: Determination of the original position (locus) of a gene or other
marker on a chromosome.
Locus (pl. loci): The position on a chromosome of a gene or other
chromosome marker; also, the DNA at that position. The use of locus is
sometimes restricted to mean regions of DNA that are expressed. See gene
expression.
Long-Range Restriction Mapping: Restriction enzymes are proteins that
cut DNA at precise locations. Restriction maps depict the positions on
chromosomes of restriction enzyme cutting sites. These are used as
biochemical "signposts", or markers of specific areas along the
chromosomes. The map will detail the positions on the DNA molecule that
are cut by particular restriction enzymes.

M
Macrorestriction map: Map depicting the order of and distance between
sites at which restriction enzymes cleave chromosomes.
Mapping: See gene mapping, linkage map, physical map.
Marker: An identifiable physical location on a chromosome (e.g., restriction
enzyme cutting site, gene) whose inheritance can be monitored. Markers can
be expressed regions of DNA (genes) or some segment of DNA with no
known coding function but whose pattern of inheritance can be determined.
See restriction fragment length polymorphism.
Mb: See megabase.
Megabase (Mb): Unit of length for DNA fragments equal to 1 million
nucleotides and roughly equal to 1 cM.
Meiosis: The process of two consecutive cell divisions in the diploid
progenitors of sex cells. Meiosis results in four rather than two daughter
cells, each with a haploid set of chromosomes.
Messenger RNA (mRNA): RNA that serves as a template for protein
synthesis. See genetic code.
Metaphase: A stage in mitosis or meiosis during which the chromosomes
are aligned along the equatorial plane of the cell.
Mitosis: The process of nuclear division in cells that produces daughter cells
that are genetically identical to each other and to the parent cell.
mRNA: See messenger RNA.
Multifactorial or multigenic disorder: See polygenic disorder .
Multiplexing: A sequencing approach that uses several pooled samples
simultaneously, greatly increasing sequencing speed.
Mutation: Any heritable change in DNA sequence. Compare polymorphism.

N Nitrogenous base: A nitrogencontaining molecule having the chemical
properties of a base.
Nucleic acid: A large molecule composed of nucleotide subunits.
Nucleotide: A subunit of DNA or RNA consisting of a nitrogenous base
(adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or
cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose
in DNA and ribose in RNA). Thousands of nucleotides are linked to form a
DNA or RNA molecule. See DNA, base pair, RNA.
Nucleus: The cellular organelle in eukaryotes that contains the genetic
material.

O
Oncogene: A gene, one or more forms of which is associated with cancer.
Many oncogenes are involved, directly or indirectly, in controlling the rate of
cell growth.
Overlapping clones: See genomic library.

P
P1-derived artificial chromosome (PAC): A vector used to clone DNA
fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli
cells. Based on bacteriophage (a virus) P1 genome. Compare cloning vector .
PAC: See P1-derived artificial chromosome.
PCR: See polymerase chain reaction .
Phage: A virus for which the natural host is a bacterial cell.
Physical map: A map of the locations of identifiable landmarks on DNA
(e.g., restriction enzyme cutting sites, genes), regardless of inheritance.
Distance is measured in base pairs. For the human genome, the lowestresolution
physical map is the banding patterns on the 24 different
chromosomes; the highest resolution map would be the complete nucleotide
sequence of the chromosomes.
Plasmid: Autonomously replicating, extrachromosomal circular DNA
molecules, distinct from the normal bacterial genome and nonessential for
cell survival under nonselective conditions. Some plasmids are capable of
integrating into the host genome. A number of artificially constructed
plasmids are used as cloning vectors.
Polygenic disorder: Genetic disorder resulting from the combined action of
alleles of more than one gene (e.g., heart disease, diabetes, and some
cancers). Although such disorders are inherited, they depend on the
simultaneous presence of several alleles; thus the hereditary patterns are
usually more complex than those of singlegene disorders. Compare singlegene
disorders.
Polymerase chain reaction (PCR): A method for amplifying a DNA base
sequence using a heatstable polymerase and two 20-base primers, one
complementary to the (+) strand at one end of the sequence to be amplified
and the other complementary to the (-) strand at the other end. Because the
newly synthesized DNA strands can subsequently serve as additional
templates for the same primer sequences, successive rounds of primer
annealing, strand elongation, and dissociation produce rapid and highly
specific amplification of the desired sequence. PCR also can be used to
detect the existence of the defined sequence in a DNA sample.
Polymerase, DNA or RNA: Enzymes that catalyze the synthesis of nucleic
acids on preexisting nucleic acid templates, assembling RNA from
ribonucleotides or DNA from deoxyribonucleotides.
Polymorphism: Difference in DNA sequence among individuals. Genetic
variations occurring in more than 1% of a population would be considered
useful polymorphisms for genetic linkage analysis. Compare mutation.
Positional Cloning: a technique used to identify genes, usually those that
are associated with diseases, based on their location on a chromosome. This
in in contrast to the older, "functional cloning" technique that relies on some
knowledge of a gene's protein product. For most diseases, researchers have
no such knowledge. For more information, see "Positional Cloning Approach
Expedites Gene Hunts" in Human Genome News, 6(6). For a list of inherited
disease genes identified by positional cloning, click here.
Primer: Short preexisting polynucleotide chain to which new
deoxyribonucleotides can be added by DNA polymerase.
Probe: Singlestranded DNA or RNA molecules of specific base sequence,
labeled either radioactively or immunologically, that are used to detect the
complementary base sequence by hybridization.
Prokaryote: Cell or organism lacking a membrane-bound, structurally
discrete nucleus and other subcellular compartments. Bacteria are
prokaryotes. Compare eukaryote. See chromosome.
Promoter: A site on DNA to which RNA polymerase will bind and initiate
transcription.
Protein: A large molecule composed of one or more chains of amino acids
in a specific order; the order is determined by the base sequence of
nucleotides in the gene coding for the protein. Proteins are required for the
structure, function, and regulation of the bodys cells, tissues, and organs,
and each protein has unique functions. Examples are hormones, enzymes,
and antibodies.
Purine: A nitrogencontaining, double-ring, basic compound that occurs in
nucleic acids. The purines in DNA and RNA are adenine and guanine.
Pyrimidine: A nitrogen-containing, single-ring, basic compound that occurs
in nucleic acids. The pyrimidines in DNA are cytosine and thymine; in RNA,
cytosine and uracil.

R
Rarecutter enzyme: See restriction enzyme cutting site.
Recombinant clone: Clone containing recombinant DNA molecules. See
recombinant DNA technology.
Recombinant DNA molecules: A combination of DNA molecules of
different origin that are joined using recombinant DNA technologies.
Recombinant DNA technology: Procedure used to join together DNA
segments in a cell-free system (an environment outside a cell or organism).
Under appropriate conditions, a recombinant DNA molecule can enter a cell
and replicate there, either autonomously or after it has become integrated
into a cellular chromosome.
Recombination: The process by which progeny derive a combination of
genes different from that of either parent. In higher organisms, this can
occur by crossing over.
Regulatory region or sequence: A DNA base sequence that controls gene
expression.
Resolution: Degree of molecular detail on a physical map of DNA, ranging
from low to high.
Restriction enzyme, endonuclease: A protein that recognizes specific,
short nucleotide sequences and cuts DNA at those sites. Bacteria contain
over 400 such enzymes that recognize and cut over 100 different DNA
sequences. See restriction enzyme cutting site.
Restriction enzyme cutting site: A specific nucleotide sequence of DNA
at which a particular restriction enzyme cuts the DNA. Some sites occur
frequently in DNA (e.g., every several hundred base pairs), others much less
frequently (rarecutter; e.g., every 10,000 base pairs).
Restriction fragment length polymorphism (RFLP): Variation between
individuals in DNA fragment sizes cut by specific restriction enzymes;
polymorphic sequences that result in RFLPs are used as markers on both
physical maps and genetic linkage maps. RFLPs are usually caused by
mutation at a cutting site. See marker.
RFLP: See restriction fragment length polymorphism.
Ribonucleic acid (RNA): A chemical found in the nucleus and cytoplasm of
cells; it plays an important role in protein synthesis and other chemical
activities of the cell. The structure of RNA is similar to that of DNA. There are
several classes of RNA molecules, including messenger RNA, transfer RNA,
ribosomal RNA, and other small RNAs, each serving a different purpose.
Ribonucleotide: See nucleotide.
Ribosomal RNA (rRNA): A class of RNA found in the ribosomes of cells.
Ribosomes: Small cellular components composed of specialized ribosomal
RNA and protein; site of protein synthesis. See ribonucleic acid (RNA).
RNA: See ribonucleic acid.

S
Sequence: See base sequence.
Sequence tagged site (STS): Short (200 to 500 base pairs) DNA
sequence that has a single occurrence in the human genome and whose
location and base sequence are known. Detectable by polymerase chain
reaction, STSs are useful for localizing and orienting the mapping and
sequence data reported from many different laboratories and serve as
landmarks on the developing physical map of the human genome. Expressed
sequence tags (ESTs) are STSs derived from cDNAs.
Sequencing: Determination of the order of nucleotides (base sequences) in
a DNA or RNA molecule or the order of amino acids in a protein.
Sex chromosome:The X or Y chromosome in human beings that
determines the sex of an individual. Females have two X chromosomes in
diploid cells; males have an X and a Y chromosome. The sex chromosomes
comprise the 23rd chromosome pair in a karyotype. Compare autosome.
Shotgun method: Sequencing method which involves randomly sequencing
tiny cloned pieces of the genome, with no foreknowledge of where on a
chromosome the piece originally came from. This can be contrasted with
"directed" strategies, in which pieces of DNA from adjacent stretches of a
chromosome are sequenced. Directed strategies eliminate the need for
complex reassembly techniques. Because there are advantages to both
strategies, researchers expect to use both random (or shotgun) and directed
strategies in combination to sequence the human genome. See library,
genomic library.
Single-gene disorder: Hereditary disorder caused by a mutant allele of a
single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell
disease). Compare polygenic disorders.
Somatic cell: Any cell in the body except gametes and their precursors.
Southern blotting: Transfer by absorption of DNA fragments separated in
electrophoretic gels to membrane filters for detection of specific base
sequences by radiolabeled complementary probes.
STS: See sequence tagged site.

T
Tandem repeat sequences: Multiple copies of the same base sequence on
a chromosome; used as a marker in physical mapping.
Technology transfer: The process of converting scientific findings from
research laboratories into useful products by the commercial sector.
Telomere: The end of a chromosome. This specialized structure is involved
in the replication and stability of linear DNA molecules. See DNA replication .
Thymine (T): A nitrogenous base, one member of the base pair AT
(adeninethymine).
Transcription: The synthesis of an RNA copy from a sequence of DNA (a
gene); the first step in gene expression. Compare translation.
Transfer RNA (tRNA): A class of RNA having structures with triplet
nucleotide sequences that are complementary to the triplet nucleotide coding
sequences of mRNA. The role of tRNAs in protein synthesis is to bond with
amino acids and transfer them to the ribosomes, where proteins are
assembled according to the genetic code carried by mRNA.
Transformation: A process by which the genetic material carried by an
individual cell is altered by incorporation of exogenous DNA into its genome.
Translation: The process in which the genetic code carried by mRNA directs
the synthesis of proteins from amino acids. Compare transcription.
tRNA: See transfer RNA.
Last
U

Uracil: A nitrogenous base normally found in RNA but not DNA; uracil is
capable of forming a base pair with adenine.

V
Vector: See cloning vector .
Virus: A noncellular biological entity that can reproduce only within a host
cell. Viruses consist of nucleic acid covered by protein; some animal viruses
are also surrounded by membrane. Inside the infected cell, the virus uses
the synthetic capability of the host to produce progeny virus.
VLSI: Very large scale integration allowing more than 100,000 transistors on
a chip.

Y
YAC: See yeast artificial chromosome.
Yeast artificial chromosome (YAC): A vector used to clone DNA
fragments (up to 400 kb); it is constructed from the telomeric, centromeric,
and replication origin sequences needed for replication in yeast cells.
Compare cloning vector.