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Glossary A single-letter designation of the purine base adenine; also used in diagrams to represent a nucleotide containing adenine Adenine a purine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter A Allele one of two or more alternative forms of a gene Allele frequency the proportion of a particular allele among the chromosomes carried by individuals in a population AMP-FLP amplified fragment length polymorphism Autoradiogram (autoradiograph; autorad) a photographic recording of the positions on a film where radioactive decay of isotopes has occurred AutosomeY any of the chromosomes other than the sex chromosomes, X and Band the visual image representing a particular DNA fragment on an autoradiogram Band shift the phenomenon in which DNA fragments in one lane of a gel migrate at a rate different from that of identical fragments in other lanes of the same gel Basepair two complementary nucleotides held together by hydrogen bonds; basepairing occurs between A and T and between G and C Biallelic (see Diallelic) Blot see Southern blot
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C single-letter designation of the pyrimidine base cytosine; also used in diagrams to represent a nucleotide containing cytosine Chromosome the structure by which hereditary information is physically transmitted from one generation to the next; the organelle that carries the genes Controls tests performed in parallel with experimental samples and designed to demonstrate that a procedure worked correctly Cytosine a pyrimidine base; one of the four nitrogen-containing molecules in nucleic acids DNA and RNA; designated by the letter C Degradation the breaking down of DNA by chemical or physical means Denaturation the process of unfolding of the complementary double strands of DNA to form single strands Deoxyribonucleic acid (DNA) the genetic material of organisms, usually double-stranded—composed of two complementary chains of nucleotides in the form of a double helix; a class of nucleic acids characterized by the presence of the sugar deoxyribose and the four bases adenine, cytosine, guanine, and thymine Diallelic DNA variation showing only two forms with a frequency of more than 1% Diploid having two sets of chromosomes, in pairs (compare haploid) DNA deoxyribonucleic acid DNA band the visual image representing a particular DNA fragment on an autoradiogram DNA databank (database) a collection of DNA typing profiles of selected or randomly chosen individuals DNA polymerase an enzyme that catalyzes the synthesis of double-stranded DNA DNA probe a short segment of single-stranded DNA labeled with a radioactive or chemical tag that is used to detect the presence of a particular DNA sequence through hybridization to its complementary sequence Electrophoresis a technique in which different molecules are separated by their rate of movement in an electric field Enzyme a protein that is capable of speeding up a specific chemical reaction but which itself is not changed or consumed in the process; a biological catalyst Ethidium bromide an organic molecule that binds to DNA and fluoresces under ultraviolet light and is used to identify DNA G single-letter designation of the purine base guanine; also used in diagrams to represent a nucleotide containing guanine Gamete a haploid reproductive cell
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Gametic (phase) equilibrium the state at loci on different chromosomes when the allele at one locus in the gamete varies independently of that at the other loci; in gametic (phase) disequilibrium, a specific allele at one locus is associated with an allele at another locus on a different chromosome with a frequency greater than expected by chance (see linkage disequilibrium) Gel semisolid matrix (usually agarose or acrylamide) used in electrophoresis to separate molecules Gene the basic unit of heredity; a sequence of DNA nucleotides on a chromosome Gene frequency the relative occurrence of a particular allele in a population Genetic drift random fluctuation in allele frequencies Genome the total genetic makeup of an organism Genotype the genetic makeup of an organism, as distinguished from its physical appearance or phenotype Guanine a purine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter G Haploid having one set of chromosomes (compare diploid) Hardy-Weinberg equilibrium the condition, for a particular genetic locus and a particular population, with the following properties: allele frequencies at the locus are constant in the population over time and there is no statistical correlation between the two alleles possessed by individuals in the population; such a condition is approached in large randomly mating populations in the absence of selection, migration, and mutation Heredity the transmission of characteristics from parent to offspring Heterozygote a diploid organism that carries different alleles at one or more genetic loci on its homologous chromosomes Heterozygous having different alleles at a particular locus; for most forensic DNA probes, the autoradiogram displays two bands if the person is heterozygous at the locus HLA see human leukocyte antigen Homology similarity between two structures or functions indicative of a common evolutionary origin Homozygote a diploid organism that carries identical alleles at one or more genetic loci on its homologous chromosomes Homozygous having the same allele at a particular locus; for most forensic DNA probes, the autoradiogram displays a single band if the person is homozygous at the locus Human leukocyte antigen (HLA) protein-sugar structures on the surface of most cells, except blood cells, that differ among individuals and are
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important for acceptance or rejection of tissue grafts or organ transplants; the locus of one particular class, HLA DQ, is used for forensic analysis with PCR Hybridization the reassociation of complementary strands of nucleic acids, nucleotides, or probes Isotope an alternative form of a chemical element; used particularly in reference to the radioactive alternative forms, or radioisotopes Linkage disequilibrium the phenomenon in which a specific allele at one locus is non-randomly associated with an allele at another locus Locus (pl. loci) the specific physical location of a gene on a chromosome Marker a gene with a known location on a chromosome and a clear-cut phenotype that is used as a point of reference in the mapping of other loci Membrane the matrix (usually nylon) to which DNA is transferred during the Southern blotting procedure Molecular-weight size marker DNA fragments of known size, from which the size of an unknown DNA sample can be determined Monomorphic probe a probe that detects the same allele and hence the same pattern in everyone Multilocus probe a DNA probe that detects genetic variation at multiple sites; an autoradiogram of a multilocus probe yields a complex, stripelike pattern of 30 or more bands per individual Mutagen a physical agent (e.g., x rays) or chemical agent that induces changes in DNA Nucleic acid a nucleotide polymer of which major types are DNA and RNA Nucleotide a unit of nucleic acid composed of phosphate, a five-carbon sugar (ribose or deoxyribose), and a purine or a pyrimidine base PCR polymerase chain reaction Phenotype the physical appearance or functional expression of a trait Point mutation an alteration of one nucleotide in chromosomal DNA that consists of addition, deletion, or substitution of nucleotides Polymerase chain reaction (PCR) an in vitro process that yields millions of copies of desired DNA through repeated cycling of a reaction that involves the enzyme DNA polymerase Polymorphism the presence of more than one allele of a gene in a population at a frequency greater than that of a newly arising mutation; opera-
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tionally, a population in which the most common allele at a locus has a frequency of less than 99% Population a group of individuals occupying a given area at a given time Probe a short segment of single-stranded DNA tagged with a reporter molecule, such as radioactive phosphorus atom, that is used to detect a particular complementary DNA sequence Proficiency tests tests to evaluate the competence of technicians and the quality performance of a laboratory; in open tests, the technicians are aware that they are being tested, but in blind tests, they are not aware; internal proficiency tests are conducted by the laboratory itself, and external tests are conducted by an agency independent of the laboratory being tested Protein a chain of amino acids joined by peptide bonds Purine the larger of two kinds of bases found in DNA and RNA; a nitrogenous base with a double-ring structure, such as adenine or guanine (compare pyrimidine) Pyrimidine the smaller of two kinds of bases found in DNA and RNA; a nitrogenous base with a single-ring structure, such as cytosine, thymine, and uracil (compare purine) Quality assurance a program conducted by a laboratory to ensure accuracy and reliability of tests performed Quality control internal activities or activities according to externally established standards used to monitor the quality of DNA typing to meet and satisfy specified criteria Recombinant DNA fragments of DNA from two different species, such as a bacterium and a mammal, spliced into a single molecule Replication the synthesis of new DNA from existing DNA Restriction endonuclease, restriction enzyme an enzyme that cleaves DNA molecules at particular base sequences Restriction fragment length polymorphism (RFLP) variation in the length of DNA fragments produced by a restriction endonuclease that cuts at a polymorphic locus RFLP restriction fragment length polymorphism RFLP analysis technique that uses single-locus or multi-locus probes to detect variation in a DNA sequence according to differences in the length of fragments created by cutting DNA with a restriction enzyme Ribonucleic acid (RNA) a class of nucleic acids characterized by the presence of the sugar ribose and the pyrimidine uracil, as opposed to the thymine of DNA RNA ribonucleic acid
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Serology the discipline concerned with the immunologic study of body fluids Serum the liquid that separates from blood after coagulation Sex chromosomes (x and y chromosomes) chromosomes that are different in the two sexes and that are involved in sex determination Sex-linked characteristic a genetic characteristic, such as color blindness, that is determined by a gene on a sex chromosome and shows a different pattern of inheritance in males and females; X-linked is a more specific term Single-locus probe a DNA probe that detects genetic variation at only one site in the genome; an autoradiogram that uses one single-locus probe usually displays one band in homozygotes and two bands in heterozygotes Somatic cells the differentiated cells that make up the body tissues of multicellular plants and animals Southern blot the nylon membrane to which DNA adheres after the process of Southern blotting Southern blotting the technique for transferring DNA fragments that have been separated by electrophoresis from the gel to a nylon membrane Standards criteria established for quality control and quality assurance; established or known test reagents, such as molecular-weight standards T single-letter designation of the pyrimidine base thymine; also used in diagrams to represent a nucleotide containing thymine Tandem repeats multiple copies of an identical DNA sequence arranged in direct succession in a particular region of a chromosome Taq polymerase a DNA polymerase used to form double-stranded DNA from nucleotides and a single-stranded DNA template in the PCR technique Thymine a pyrimidine base; one of the four nitrogen-containing molecules present in nucleic acids DNA and RNA; designated by the letter T Uracil a pyrimidine in RNA Variable number of tandem repeats (VNTR) repeating units of a DNA sequence for which the number varies between individuals VNTR variable number of tandem repeats Zygote diploid cell that results from the fusion of male and female gametes
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