Genome Project - Primer on molecular genetics - 1992 (522926), страница 9
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Compare polymorphism.Nitrogenous base: A nitrogen-containing molecule having the chemical properties of abase.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.Oncogene: A gene, one or more forms of which is associated with cancer.
Manyoncogenes are involved, directly or indirectly, in controlling the rate of cell growth.Overlapping clones: See genomic library.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., restrictionenzyme cutting sites, genes), regardless of inheritance.
Distance is measured in basepairs. For the human genome, the lowest-resolution physical map is the banding patternson the 24 different chromosomes; the highest-resolution map would be the completenucleotide sequence of the chromosomes.Plasmid: Autonomously replicating, extrachromosomal circular DNA molecules, distinctfrom the normal bacterial genome and nonessential for cell survival under nonselectiveconditions. Some plasmids are capable of integrating into the host genome.
A number ofartificially constructed plasmids are used as cloning vectors .Polygenic disorders: Genetic disorders resulting from the combined action of alleles ofmore than one gene (e.g., heart disease, diabetes, and some cancers). Although suchdisorders are inherited, they depend on the simultaneous presence of several alleles; thusthe hereditary patterns are usually more complex than those of single-gene disorders.Compare single-gene disorders.Polymerase chain reaction (PCR): A method for amplifying a DNA base sequence usinga heat-stable polymerase and two 20-base primers, one complementary to the (+)-strandat one end of the sequence to be amplified and the other complementary to the (–)-strandat the other end. Because the newly synthesized DNA strands can subsequently serveas additional templates for the same primer sequences, successive rounds of primer39Glossaryannealing, 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 definedsequence in a DNA sample.Polymerase, DNA or RNA: Enzymes that catalyze the synthesis of nucleic acids onpreexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA fromdeoxyribonucleotides.Polymorphism: Difference in DNA sequence among individuals. Genetic variationsoccurring in more than 1% of a population would be considered useful polymorphisms forgenetic linkage analysis. Compare mutation.Primer: Short preexisting polynucleotide chain to which new deoxyribonucleotides can beadded by DNA polymerase.Probe: Single-stranded DNA or RNA molecules of specific base sequence, labeledeither radioactively or immunologically, that are used to detect the complementary basesequence by hybridization.Prokaryote: Cell or organism lacking a membrane-bound, structurally discrete nucleusand other subcellular compartments.
Bacteria are prokaryotes. Compare eukaryote. Seechromosomes.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 specificorder; the order is determined by the base sequence of nucleotides in the gene coding forthe protein. Proteins are required for the structure, function, and regulation of the body’scells, tissues, and organs, and each protein has unique functions. Examples are hormones, enzymes, and antibodies.Purine: A nitrogen-containing, single-ring, basic compound that occurs in nucleic acids.The purines in DNA and RNA are adenine and guanine.Pyrimidine: A nitrogen-containing, double-ring, basic compound that occurs in nucleicacids.
The pyrimidines in DNA are cytosine and thymine; in RNA, cytosine and uracil.Rare-cutter enzyme: See restriction enzyme cutting site.Recombinant clones: Clones containing recombinant DNA molecules. See recombinantDNA technologies.Recombinant DNA molecules: A combination of DNA molecules of different origin thatare joined using recombinant DNA technologies.40Recombinant DNA technologies: Procedures used to join together DNA segments in acell-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 differentfrom that of either parent.
In higher organisms, this can occur by crossing over.Regulatory regions or sequences: A DNA base sequence that controls gene expression.Resolution: Degree of molecular detail on a physical map of DNA, ranging from low tohigh.Restriction enzyme, endonuclease: A protein that recognizes specific, short nucleotidesequences and cuts DNA at those sites. Bacteria contain over 400 such enzymes thatrecognize and cut over 100 different DNA sequences. See restriction enzyme cutting site.Restriction enzyme cutting site: A specific nucleotide sequence of DNA at which aparticular restriction enzyme cuts the DNA.
Some sites occur frequently in DNA (e.g.,every several hundred base pairs ), others much less frequently (rare-cutter; e.g., every10,000 base pairs).Restriction fragment length polymorphism (RFLP): Variation between individuals inDNA fragment sizes cut by specific restriction enzymes; polymorphic sequences thatresult 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 playsan 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, eachserving a different purpose.Ribonucleotides: See nucleotide.Ribosomal RNA (rRNA): A class of RNA found in the ribosomes of cells.Ribosomes: Small cellular components composed of specialized ribosomal RNA andprotein; site of protein synthesis.
See ribonucleic acid (RNA ).RNA: See ribonucleic acid.Sequence: See base sequence.41GlossarySequence tagged site (STS): Short (200 to 500 base pairs ) DNA sequence that has asingle occurrence in the human genome and whose location and base sequence areknown. Detectable by polymerase chain reaction, STSs are useful for localizing andorienting the mapping and sequence data reported from many different laboratories andserve as landmarks on the developing physical map of the human genome. Expressedsequence tags (ESTs) are STSs derived from cDNAs.Sequencing: Determination of the order of nucleotides ( base sequences) in a DNA orRNA molecule or the order of amino acids in a protein.Sex chromosomes: The X and Y chromosomes in human beings that determine the sexof an individual.
Females have two X chromosomes in diploid cells; males have an X anda Y chromosome. The sex chromosomes comprise the 23rd chromosome pair in akaryotype. Compare autosome.Shotgun method: Cloning of DNA fragments randomly generated from a genome. Seelibrary, 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). Comparepolygenic disorders.Somatic cells: Any cell in the body except gametes and their precursors.Southern blotting: Transfer by absorption of DNA fragments separated in electrophoreticgels to membrane filters for detection of specific base sequences by radiolabeled complementary probes.STS: See sequence tagged site.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 ends of chromosomes.
These specialized structures are involved in thereplication and stability of linear DNA molecules. See DNA replication.Thymine (T): A nitrogenous base, one member of the base pair A-T (adenine-thymine).Transcription: The synthesis of an RNA copy from a sequence of DNA (a gene); the firststep in gene expression. Compare translation.Transfer RNA (tRNA): A class of RNA having structures with triplet nucleotide sequencesthat are complementary to the triplet nucleotide coding sequences of mRNA.
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