Page 214

Glossary1

A

Adeninea purine base; one of the constituents of DNA; abbreviated A.

Alleleone of two or more alternative forms of a gene. In DNA analysis the definition is extended to any DNA region used for analysis.

Amplificationincreasing the number of copies of a DNA region, usually by PCR.

Autoradiograph (autoradiogram; autorad)a photographic recording of the position on an X-ray film where radioactive decay of isotopes has occurred.

Autosomeany chromosome other than the X or Y.

B

Bandthe visual image representing a particular DNA fragment on an autoradiograph.

Band shift—the phenomenon in which DNA fragments in one lane of a gel migrate at a different rate from that of identical fragments in other lanes of the same gel.

Base pairtwo complementary nucleotides in double-stranded DNA; these are AT or GC.

Biasedsystematically deviating from the true value, as a conservative estimate.

Binninggrouping VNTR alleles into sets of similar sizes, necessary because the individual alleles are too similar to differentiate; two binning processes are fixed and floating bins (see Chapter 5).

Blind proficiency testa proficiency test in which the laboratory personnel do not know that a test is being conducted.

Blotsee Southern blot.

1Adapted from NRC (1992).



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 214
Page 214 Glossary1 A Adenine—a purine base; one of the constituents of DNA; abbreviated A. Allele—one of two or more alternative forms of a gene. In DNA analysis the definition is extended to any DNA region used for analysis. Amplification—increasing the number of copies of a DNA region, usually by PCR. Autoradiograph (autoradiogram; autorad)—a photographic recording of the position on an X-ray film where radioactive decay of isotopes has occurred. Autosome—any chromosome other than the X or Y. B Band—the visual image representing a particular DNA fragment on an autoradiograph. Band shift—the phenomenon in which DNA fragments in one lane of a gel migrate at a different rate from that of identical fragments in other lanes of the same gel. Base pair—two complementary nucleotides in double-stranded DNA; these are AT or GC. Biased—systematically deviating from the true value, as a conservative estimate. Binning—grouping VNTR alleles into sets of similar sizes, necessary because the individual alleles are too similar to differentiate; two binning processes are fixed and floating bins (see Chapter 5). Blind proficiency test—a proficiency test in which the laboratory personnel do not know that a test is being conducted. Blot—see Southern blot. 1Adapted from NRC (1992).

OCR for page 214
Page 215 C Chromosome—a physical structure in the cell nucleus, made of DNA, RNA, and proteins. The genes are arranged in linear order along the chromosome. Ceiling principle—a procedure for setting a minimum profile frequency. One hundred persons from each of 15-20 genetically homogeneous populations spanning the range of racial groups in the United States are sampled. For each allele, the highest frequency among the groups sampled, or 5%, whichever is larger, is used for calculations. (cf. interim ceiling principle) Confidence interval, confidence limits—An interval, based on a sample, that is expected to include the population mean value a specified proportion of the time. 100(1-a)% confidence limits are expected to include the population value 100(1-a)% of the time. Conventional values are 90% (a = 0.10), 95%, and 99%. Conservative—favoring the defendant. A conservative estimate is deliberately chosen to be more favorable to the defendant than the best (unbiased) estimate would be. Convenience sample—a sample chosen because of availability or similar reason; not a random sample. Covariance (Cov, C)—for paired numbers, the average of the product of the deviation from its mean of each member of a pair. Crossing over—the exchange of parts between homologous chromosomes during meiosis; recombination. Cytosine—a pyrimidine base; one of the constituents of DNA; abbreviated C. D Degradation—the breaking down of DNA by chemical or physical means. Denaturation—separation of a double stranded DNA into single strands. Deoxyribonucleic acid (DNA)—the genetic material; a double helix composed of two complementary chains of paired nucleotides. Diploid—having two sets of chromosomes (cf. haploid). DNA polymerase—the enzyme that catalyzes the synthesis of double-stranded DNA. DNA probe—see probe. E EDTA—a preservative added to blood samples. 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, and therefore facilitating, a specific chemical reaction; a biological catalyst. Ethidium bromide—a molecule that binds to DNA and fluoresces under ultraviolet light; used to identify DNA. F F statistics—Wright's measures of inbreeding and population structure; in this report population subdivision is measured by FST or . G Gamete—a haploid reproductive cell; sperm or egg. Gametic equilibrium—see linkage equilibrium. Gel—a semisolid medium used to separate molecules by electrophoresis. Gene—the basic unit of heredity; a functional sequence of DNA in a chromosome.

OCR for page 214
Page 216 Gene frequency—the relative frequency (proportion) of an allele in a population. Genetic drift—random fluctuation in allele frequencies. Genome—the total (haploid) genetic makeup of an organism. In the human this comprises 3 billion base pairs. Genotype—the genetic makeup of an organism, as distinguished from its physical appearance (phenotype); usually designated by allele symbols, e.g., A1A2 designates the genotype of an individual with alleles A1 and A2. The word may be used to designate any number of loci, from one to the total number. Guanine—a purine base; one of the consituents of DNA; abbreviated G. H Haploid—having one set of chromosomes, as a gamete (cf. diploid). Hardy-Weinberg proportions—the state, for a genetic locus in a population, in which the alleles making up the genotypes are in random proportions; abbreviated HW. Heterozygosity—the proportion of a population that is heterozygous for a particular locus. Heterozygote—a fertilized egg (zygote) with two different alleles at a designated locus; by extension, the individual that develops from such a zygote. Heterozygous—having different alleles at a particular locus (cf. homozygous). Homologous—corresponding; used to describe the relationship between two members of a chromosome or gene pair. Homozygote—a fertilized egg (zygote) with two identical alleles at a designated locus; by extension, the individual that develops from such a zygote. Homozygous—having the same allele at a particular locus (cf. heterozygous). Hybridization—the pairing of complementary single strands of DNA. I Inbreeding coefficient—the probability that two homologous genes in an individual are descended from the same gene in an ancestor; a measure of the proportion by which the heterozygosity is reduced by inbreeding; designated by F. Interim ceiling principle—For each allele, the highest frequency (adjusted upward for statistical uncertainty) found in any racial group, or 10%, whichever is higher, is used in product-rule calculations. (cf. ceiling principle) Isotope—an alternative form of a chemical element; used particularly in reference to radioactive forms, or radioisotopes. K Kilobase (kb)—1,000 bases. Kinship coefficient—the probability that two randomly chosen genes, one from each of two individuals in a population, are identical (i.e. both descended from the same ancestral gene, or one from the other); equivalent to the inbreeding coefficient of a (perhaps hypothetical) offspring; designated by F. L Linkage—inheritance together of two or more genes on the same chromosome. Linkage equilibrium—the state in which two or more loci in a gamete are in random proportions (i.e., the gamete frequency is the product of the allele frequencies; abbreviated LE). Locus (pl. loci)—the physical location of a gene on a chromosome.

OCR for page 214
Page 217 M Marker—an easily detected gene or chromosome region used for identification. Match—Two DNA profiles are declared to match when they are indistinguishable in genetic type. For loci with discrete alleles, two samples match when they display the same set of alleles. For VNTRs, two samples match when the pattern of the bands are similar and the positions of the corresponding bands at each locus fall within a preset distance. Meiosis—the two cell divisions that occur in the development of a sperm or egg, during which the chromosome number is halved. Membrane—the matrix (usually nylon) to which DNA is transferred from a gel during Southern blotting. N Nucleic acid—DNA or RNA. Nucleotide—a unit of nucleic acid composed of phosphate, a sugar, and a purine or pyrimidine base. P Phenotype—the manifestation of the genotype; it may be externally visible, as eye color, or observed by a special technique, as blood groups or enzymes. Polymerase chain reaction—an in vitro process for making many copies of a fragment of DNA; abbreviated PCR. Polymorphism—the presence of more than one allele at a locus in a population; in forensic loci, the most common allele usually has a frequency less than 0.6. 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. Proficiency test—a test to evaluate the quality of performance of a laboratory. Purine—the larger of the two kinds of bases found in DNA and RNA; A and G are purines. Pyrimidine—the smaller of the two kinds of bases found in DNA and RNA; C and T are pyrimidines. Q Quality assurance—a program conducted by a laboratory to ensure accuracy and reliability of tests performed; abbreviated QA. Quality audit—a systematic and independent examination and evaluation of a laboratory's operations. Quality control—activities used to monitor the quality of DNA typing to satisfy specified criteria; abbreviated QC. R Random match—A match in the DNA profiles of two samples of DNA, where one is drawn at random from the population. Random-match probability—The chance of a random match. As used in this report, it is the probability that the DNA in a random sample from the population has the same profile as the DNA in the evidence sample. Random sample—a sample chosen so that each sample of the population has a known chance of being represented. In a simple random sample each member has an equal chance of being represented. Rebinning—grouping adjacent bins whose absolute number in the data base is fewer than five.

OCR for page 214
Page 218 Replication—the synthesis of new DNA from existing DNA. Restriction enzyme, restriction endonuclease—an enzyme that cuts a DNA molecule at a specified short base sequence. Restriction fragment length polymorphism—variation in the length of a stretch of DNA; abbreviated RFLP. Ribonucleic acid—a class of nucleic acid; it is synthesized from DNA and is part of the process of translating a DNA sequence into a phenotype; abbreviated RNA. S Sex chromosomes—the X and Y chromosomes. Short tandem repeat—a tandem repeat in which the repeat units are three, four, or five base pairs; abbreviated STR. Significant, statistically significant—two values are significantly different if the probability of obtaining a difference as large as or larger than that found is less than a when the true difference is zero. Conventionally, a is taken as 0.05, although other values, such as 0.01, are also used. Somatic cells—cells other than those in the cellular ancestry of egg and sperm. Southern blotting—the technique for transferring DNA fragments that have been separated by electrophoresis from the gel to a nylon membrane. Standard deviation—the square root of the variance; abbreviated s or s. T Tandem repeat—multiple copies of an identical DNA sequence arranged in direct succession in a particular region of the chromosome. Thymine—a pyrimidine base; one of the constituents of DNA; abbreviated T. V Variable number of tandem repeats—repeating units of a DNA sequence; a class of RFLPs; abbreviated VNTR. Variance (Var, V)—for a series of numbers, the average of the squared deviation of each number from the mean. Z Zygote—the diploid cell resulting from the fusion of egg and sperm.