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The following Scientific Terms are defined as follows:
Adenine (A)
A nitrogenous base, one member of the base pair AT (adenine, thymine)
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
One of the 20 different organic molecules that are joined together to form a polypeptide chain. The polypeptide chain then folds into a compact, globular three-dimensional structure that is a functional protein. This three-dimensional conformation is held together by the interactions of the amino acids at different parts of the polypeptide chain with each other, and determines the activity of the protein. Thus, the amino acid order and content determines the shape and functional activity of the protein.
Amplification
An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro.
Antibody
A type of protein, also known as immunoglobulin, produced by the body normally to fight infection. Several classes of antibodies are known; IgG, IgE, IgA, IgM, IgD. Antibodies are present in the blood and other bodily secretions. In certain disease states (eg.auto-immune disease) antibodies are made that attack the body by forming immune complexes.
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.
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).
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.
Base pair
The chemical structures that form the units of DNA and RNA and that encode genetic information i.e. the bases that make up the base-pairs are A, G, T, C and U (see DNA). Strictly, a base pair is a pair of complementary bases (i.e. the A:T, G:C and A:U interactions) held together by hydrogen bonds. However, this term is used loosely as a measure of DNA and RNA length (although RNA is single-stranded). The term is also used interchangeably with "nucleotide" although the latter is composed of a five-carbon sugar joined to a phosphate group and one of the bases.
Bioinformatics
The collection, organisation and analysis of large amounts of biological data, using networks of computers and databases. Historically, bioinformatics concerned itself with the analysis of the sequences of genes and their products (proteins), but the field has since expanded to the management, processing, analysis and visualisation of large quantities of data from genomics, proteomics, drug screening and medicinal chemistry. Bioinformatics also includes the integration and "mining" (detailed searching) of the ever-expanding databases of information from these disciplines.
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.
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 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 organisms.
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.
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 double-stranded 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.
Cytosine (C)
A nitrogenous base, one member of the base pair GC (guanine and cytosine).
Chromosomes
The self-replicating genetic structures of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes.
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.
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.
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.
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.
DNA (Deoxyribonucleic Acid)
The chemical that forms the basis of the genetic material in virtually all living organisms. Structurally, DNA is composed of two strands that intertwine to form a spring-like structure called the double helix. Each strand is formed by a backbone of deoxyribose sugar molecules linked by phosphate residues. Attached to each backbone are chemical structures called bases, which protrude away from the backbone towards the center of the helix, and which come in four types - Adenine, Cytosine, Guanine, and Thymine (designated A, C, G and T). Each strand of DNA has a series of Gs, As, Ts and Cs attached to its backbone. It is the sequence of these bases that forms the code which is translated by cellular machinery to create a new protein.
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.
Eukaryote
Cell or organism with membrane bound, structurally discrete nucleus and other well developed sub-cellular compartments. Eukaryotes include all organisms except viruses, bacteria, and bluegreen algae.
Exogenous DNA
DNA originating outside an organism
Exon
The protein coding DNA sequence of a gene.
Exonuclease
An enzyme that cleaves nucleotides sequentially from free ends of a linear nucleic acid substrate.
FISH (fluorescence in situ hybridization)
A physical mapping approach that uses fluorescein tags to detect hybridization of probes with metaphase chromosomes and with the less condensed somatic interphase chromatin.
Flow cytometry
Analysis of biological material by detection of the light absorbing or fluorescing properties of cells or sub-cellular 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.
Food and Drug Administration (FDA)
The USA government regulatory body responsible for the safety and regulation of new medicines.
Functional Genomics
The use of genetic technology to determine the function of newly discovered genes by determining their role in one or more model organisms. Functional genomics uses as its starting point the isolated gene whose function is to be determined, and then selects a model organism in which a homolog of that gene exists. This model organism can be as simple as a yeast cell or as complex as a nematode worm, fruitfly, or even a mouse. The gene is selectively inactivated or "knocked out" using a variety of genetic techniques, and the effect of its selective deletion on that organism is determined. By knocking out a gene in this way, its contribution to the function of the organism (and, by implication, its function in man), can be determined. Functional genomics has proven particularly useful as a means of validating or testing novel therapeutic targets.
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).
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 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 disease causing 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.
Genetics
The study of the patterns of inheritance of specific traits.
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.
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).
Gene Therapy
The technology that uses genetic material for therapeutic purposes. This genetic material can be in the form of a gene, a representative of a gene or even a small fragment of a gene. The introduced genetic material can be therapeutic in several ways: It can make a protein that is defective or missing in the patient's cells (as would be the case for a genetic disorder), or one which will correct or modify a particular cellular function, or a protein that elicits an immune response. In gene therapy approaches, the genetic material may be introduced into the patient in several different ways. It can be directly injected for some applications in a process known as genetic vaccination, or it can be introduced by using bioengineered viruses that will carry the therapeutic gene as part of their own genetic cargo and deliver it into the cell.
Genome
All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.
Genomics
The study of genomes, which includes genome mapping, gene sequencing and gene function.
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.
Haplotype
A specific combination of single nucleotide polymorphisms (SNPs) associated with a particular gene used to measure genetic variability. Haplotypes are a convenient way to organise genetic variation and particular haplotypes can be correlated with drug response.
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.
Human gene therapy
Insertion of normal DNA directly into cells to correct a genetic defect.
Hybridization
The process of joining two complementary strands of DNA or one each of DNA and RNA to form a double-stranded molecule.
Homologous genes
A pair of genes from different but related species which correspond to each other and which are identical or very similar to each other.
Immune Complex
A complex of antibody molecules produced in response to infection or in autoimmune disease. Such complexes can invoke powerful inflammatory responses esepcially in autoimmune diseases in blood vessels, organs and joints and can lead to the destruction of whole cells, tissues and organs.
Immune Response
The natural response to a foreign substance (eg. virus, bacteria). Responses involve many of the white blood cells, including T and B lymphocytes, macrophages, neutrophils, eosinophils and platelets.
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.
in silico
Biological discovery using a computer.
In vitro
Outside a living organism.
in vivo
Within a living organism.
Karyotype
A photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type; used in low-resolution physical mapping to correlate gross chromosomal abnormalities with the characteristics of specific diseases.
Kilobase (kb)
Unit of length for DNA fragments equal to 1000 nucleotides.
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.
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.
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.
Macrorestriction map
Map depicting the order of and distance between sites at which restriction enzymes cleave chromosomes.
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.
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.
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.
Multiplexing
A sequencing approach that uses several pooled samples simultaneously, greatly increasing sequencing speed.
Mutation
Any heritable change in DNA sequence.
Nitrogenous base
A nitrogencontaining molecule having the chemical properties of a base.
NSAIDS
Non-steroidal anti-inflammatory drugs including but not limited to aspirin, ibuprofen, indomethacin, ketoprofen and naproxan that reduce inflammation, pain and swelling.
Nucleic acid
A large molecule composed of nucleotide subunits.
Nucleus
The cellular organelle in eukaryotes that contains the genetic material.
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.
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.
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.
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 lowest-resolution 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, extra-chromosomal 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 single gene disorders.
Polymerase chain reaction (PCR)
A method for amplifying a DNA base sequence using a heat stable 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.
Positional Cloning
A technique used to identify genes, usually those that are associated with diseases, based on their location on a chromosome. This is 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.
Primer
Short pre-existing polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase.
Probe
Single stranded 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 sub-cellular compartments. Bacteria are prokaryotes.
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 body's cells, tissues, and organs, and each protein has unique functions. Examples are hormones, enzymes, and antibodies.
Proteomics
The study of the entire protein complement or "protein universe" of the cell. Mirroring genomics, proteomics aims to determine the entire suite of expressed proteins in a cell. This includes determining the number, level and turnover of all expressed proteins, their sequence and any post-translational modifications to the sequence, and protein-protein and protein-other molecule interactions within the cell, across the cell membrane, and among extracellular (secreted) proteins. Methods for proteomics analysis include isolating and extracting proteins (via two-dimensional electrophoresis or high-performance liquid chromatography); determining their partial or complete sequence (via mass spectrometry); and determining their function and interactions with other molecules. The correlation of proteomics data with genomics data is expected to help to validate the many new potential targets emerging from this discipline.
Purine
A nitrogen containing, 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.
Recombinant clone
Clone containing recombinant DNA molecules.
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
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.
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.
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.
Sequencing
Sequencing refers to the delineation of the order of the repeating units in DNA and protein. Both DNA and proteins are composed of chains containing repeating units. For DNA, these units are the C, T, A and G bases, and for proteins the units are 20 different amino acids. In both cases, the sequence of the repeating units is a critical part of the information carried by these molecules. In DNA, the sequence of bases forms the code that is converted to make protein, and for proteins the arrangement of amino acids determines the protein's structure and function. For DNA, copies of the DNA to be sequenced are made and labeled with fluorescent markers before they are identified using a sequencing machine. For proteins, single amino acid residues are removed from one end of the protein and identified one at a time using an automated system.
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.
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.
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.
Single-gene disorder
Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease).
Single Nucleotide Polymorphism (SNP)
The most common genetic differences among individuals resulting from minute, single-base changes in the genetic code.
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.
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.
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.
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.
Uracil
A nitrogenous base normally found in RNA but not DNA; uracil is capable of forming a base pair with adenine.
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.
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.