Recombinant DNA Paper Plasmid Lab
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Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Characterization, or ''typing," of deoxyribonucleic modeling recombinant dna technology lab answer key DNA for purposes of criminal investigation can be thought of as an extension of the forensic typing of blood that has been common for more than 50 years; it is modeling recombinant dna technology lab answer key an extension from the typing of proteins that are coded for by DNA to the typing of DNA itself.
Genetically determined variation in proteins is the basis of blood groups, tissue types, and serum protein types. Developments in molecular genetics have made it possible to study the person-to-person differences in parts of DNA that are not involved in coding for proteins, and it is primarily these differences that are used in forensic applications of DNA typing to personal identification.
DNA typing can be a powerful adjunct to forensic science. The method was first used in casework in in the United Kingdom and first used in the United States by commercial laboratories in late and by the Federal Bureau of Investigation FBI in DNA typing has great potential benefits for criminal and civil justice; however, because of the possibilities for its misuse or abuse, important questions have been raised about reliability, validity, and confidentiality.
By the summer ofthe scientific, modeling recombinant dna technology lab answer key, and forensic communities were calling for an examination of the issues by the National Research Council of the National Academy of Sciences. The committee was to address the general applicability and appropriateness of the use of DNA technology in forensic science, the need to develop standards for data collection and analysis, aspects of the.
The techniques of DNA typing are fruits of the revolution in molecular biology that is yielding an explosion of information about human genetics. The highly personal and sensitive information that can be generated by DNA typing requires strict confidentiality and careful attention to the security of data. DNA, the active substance of the genes, carries the coded messages of heredity in every living thing: In humans, the code-carrying DNA occurs in all cells that have a nucleus, including white blood cells, sperm, cells surrounding hair roots, and cells in saliva.
These would be the cells of greatest interest in forensic studies. Human genes are carried in 23 pairs of chromosomes, long threadlike or rodlike structures that are a person's archive of heredity. Those 23 pairs, the total genetic makeup of a person, are referred to as the human "diploid genome.
The genetic code itself is spelled out in strings of nucleotides of four types, commonly represented by the letters A, C, G, and T standing for the bases adenine, cytosine, guanine, and thymine modeling recombinant dna technology lab answer key, which in various combinations of three nucleotides spell out the. The line shown in the chromosome is expanded to show the DNA structure.
A gene, the basic unit of heredity, is a sequence of about 1, to over 2 million nucleotides. The human genome, the total genetic makeup of a person, is estimated to contain 50, genes. The total number of nucleotides in a set of 23 chromosomes—one from each pair, the "haploid genome"—is about 3 billion. Much of the DNA, the part that separates genes from one another, is noncoding. Variation in the genes, the coding parts, are usually reflected in variations in the proteins that they encode, which can be recognized as "normal variation" in blood type or in the presence of such diseases as cystic fibrosis and phenylketonuria; but variations in the noncoding parts of DNA have been most useful for DNA typing.
Except for identical twins, the DNA of a person is for practical purposes unique. That is because one chromosome of each pair comes from the father and one from the mother; which chromosome of a given pair of a parent's chromosomes that parent contributes to the child is independent of which chromosome of another pair that parent gives to that child.
Thus, the different combinations of chromosomes that one parent can give to one child is 2 23and the number of different combinations of paired chromosomes a child can receive from both parents is 2 The substitution of even one nucleotide in the sequence of DNA is a variation that can be detected. For example, a modeling recombinant dna technology lab answer key in DNA consisting of the substitution of one nucleotide for another such as the substitution of a C for a T can often be recognized by a change in the points at which certain biological catalysts called "restriction enzymes" cut the DNA.
Such an enzyme cuts DNA whenever it encounters a specific sequence of nucleotides that is peculiar to the enzyme. A restriction enzyme will cut a sample of DNA into fragments whose lengths depend on the location of the cutting sites recognized by the enzyme.
Assemblies of fragments of different lengths are called "restriction fragment length polymorphisms" RFLPsand RFLPs constitute one of the most important tools for analyzing and identifying samples of DNA. An important technique used in such analyses is the "Southern blot," developed by Edwin Southern in A sample of DNA is cut with a restriction enzyme, and the fragments are separated from one another modeling recombinant dna technology lab answer key electrophoresis i.
The fragments of particular interest are then identified with a labeled probe, a short segment of single-stranded DNA containing a radioactive atom, which hybridizes fuses to the fragments of interest because its DNA sequence is complementary to those of the fragments A pairing with T, C pairing with G. Each electrophoretic band represents a separate fragment of DNA, and a given person will have no more than two fragments derived from a partic. Modeling recombinant dna technology lab answer key forms of a given gene are referred to as alleles.
A person who received the same allele from the mother and the father is said to be "homozygous" for that allele; a person who received different alleles from the mother and the father is said to be "heterozygous. They are said to be "diallelic," because there are only two common alternative forms. And there are only three genotypes: When such a structure is subjected to cutting with restriction enzymes, fragments of varied length are obtained. A locus is a specific site of a gene on a chromosome.
In the United States, in particular, single-locus probes are preferred, because their results are easier to interpret. Discriminating power for personal identification is achieved by using several—usually at least four—single-locus, multiallelic systems. After the bands alleles are visualized, those in the evidence sample and the suspect sample are compared. If the bands match in the two samples, for all three modeling recombinant dna technology lab answer key four enzyme-probe combinations, the question is: What is the probability that such a match would have occurred between the suspect and a person drawn at random from the same population as the suspect?
Answering that question requires calculation of the frequency in the population of each of the gene variants alleles that have been found, and the calculation requires a databank where one modeling recombinant dna technology lab answer key find the frequency of each allele in the population. On the basis of some assumptions, so-called Hardy-Weinberg ratios can be calculated. Suppose that a person is heterozygous at a locus where the frequencies of the two alleles in the population are 0.
Suppose, further, that at three. In example shown here, DNA from four persons is tested. All have different patterns. Three are heterozygous and one homozygous, for a total of seven different alleles. Reprinted with permission of W. The frequency of the combined genotype in the population is 0. That example illustrates what is called the product rule, or multiplication rule. Its use assumes that the alleles at a given locus are inherited independently of each other.
It also assumes that there are no subpopulations in which a particular allele at one locus would have a preferential probability of being associated with a particular allele at a second locus. Techniques for analyzing DNA are changing rapidly. One key modeling recombinant dna technology lab answer key introduced in the last few years is the polymerase chain reaction PCRwhich allows a million or more copies of a short region of DNA to be easily made. For DNA typing, one amplifies copies a genetically informative sequence, usuallynucleotides long, and detects the genotype in the amplified product.
Because many copies are made, DNA. Furthermore, the technique of PCR amplification permits the use of very small samples of tissue or body fluids—theoretically even a single nucleated cell. It can be used in conjunction with various methods for detecting person-to-person differences in DNA. It must be emphasized that new methods and technology for demonstrating individuality in each person's DNA are being developed.
The present methods explained here will probably be superseded by others that are more efficient, error-free, automatable, and cost-effective. Care should be taken to ensure that DNA typing techniques used for forensic purposes do not become "locked in" prematurely, lest society and the criminal justice system be unable to benefit fully from advances in science and technology. The forensic use of Modeling recombinant dna technology lab answer key typing is an outgrowth of its medical diagnostic use—analysis of disease-causing genes based on comparison of a patient's DNA with that of family members to study inheritance patterns of genes or comparison with reference standards to detect mutations.
To understand the challenges involved in such technology transfer, it is instructive to compare forensic DNA typing with DNA diagnostics. DNA diagnostics usually involves clean tissue samples from known sources. Its procedures can usually be repeated to resolve ambiguities.
It involves comparison of discrete modeling recombinant dna technology lab answer key e. It requires no knowledge of the distribution of patterns in the general population. Forensic DNA typing often involves samples that are degraded, contaminated, or from multiple unknown sources. Its procedures sometimes cannot be repeated, because there is too little sample.
It often involves matching of samples from a wide range of alternatives in the population and thus lacks built-in consistency modeling recombinant dna technology lab answer key. Except in cases where the DNA evidence excludes a suspect, assessing the significance of a result requires statistical analysis of population frequencies.
Each method of DNA typing has its own advantages and limitations, and each is at a different state of technical development. However, the use of each method involves three steps:. Laboratory analysis of samples to determine their genetic-marker types at multiple sites of potential variation. If the types match, statistical analysis of the population frequencies of the types to determine the probability that a match would have been observed by chance in a comparison of samples from different persons.
Before any particular DNA typing method is used for forensic purposes, precise and scientifically reliable procedures for performing all three steps must be established. It is modeling recombinant dna technology lab answer key to speak of the reliability of DNA typing in general—i. Despite the challenges of forensic DNA typing, it is possible to develop reliable forensic DNA typing systems, provided that adequate scientific care is taken to define and characterize the methods.
Any new DNA typing method or a substantial variation of an existing method must be rigorously characterized in both research and forensic settings, to determine the circumstances under which it will yield reliable results. DNA analysis in forensic science should be governed by the highest standards of scientific rigor, including the following requirements:.
Each DNA typing procedure must be completely described in a detailed, written laboratory protocol. Each DNA typing procedure requires objective and quantitative rules for identifying the pattern of a sample. Each DNA typing procedure requires a precise and objective matching rule for declaring whether two samples match. Potential artifacts should be identified by empirical testing, and scientific controls should be designed to serve as internal checks to test for the occurrence of artifacts.
The limits of each DNA typing procedure should be modeling recombinant dna technology lab answer key, especially when the DNA sample is small, is a mixture of DNA from multiple sources, or is contaminated with interfering substances.
Empirical characterization of a DNA typing procedure must be published in appropriate scientific journals.
Before a new Modeling recombinant dna technology lab answer key typing procedure can be used, it must have not only a solid scientific foundation, but also a solid base of experience. Novel forms of variation in the genome that have the potential for increased power of discrimination between persons are being discovered.
Furthermore, new ways to demonstrate variations in the genome are being developed. The current techniques are likely to be superseded by others that provide unambiguous individual identification and have such advantages as automatability and economy.
Each new method should be evaluated by the NCFDT for use in the forensic setting, applying appropriate criteria to ensure that society derives maximal benefit from DNA typing technology. Because any two human genomes differ at about 3 million sites, no two persons barring identical twins have the same DNA sequence.