What is DNA Testing?
DNA is the most powerful tool available for identification in forensic investigations. Because of its ability to link physical evidence found at a crime scene to a single person, it is often referred to as a “digital fingerprint.” This method is so precise that it can ensure pinpoint accuracy, down to one in a billion. And, unlike fingerprints, which can only be found if a suspect touches something, DNA exists in every cell of the human body, from hair and blood to skin and tears, and can be shed or deposited while committing a crime. That means it is often the only means for accurate identification.
DNA databases make it possible for law enforcement crime laboratories to electronically search and compare collected DNA profiles to crime scene evidence. In the United States, the Combined DNA Index System (CODIS) links all local, state, and national databases and contains more than 5 million records. Currently, legislation exists on the federal level and in 29 states, enabling investigators to collect DNA upon arrest for certain felony crimes.
Genes are the blueprints of heredity. Genes are made of hundreds to thousands of DNA bases.
Each gene directs cells to produce one or more specific proteins, including enzymes and structural proteins.
The human genome is the complete set of genes that every person inherits from his or her parents. It is present in virtually every cell of the body.
The human genome consists of tens of thousands of pairs of genes. Each person inherits one copy of each gene from each parent.
Genes are organized along string-like structures called chromosomes. Each individual inherits two sets of twenty-three chromosomes, one from each parent: two sets of twenty-two autosomes and one set of sex chromosomes (X, X or X, Y).
The DNA base sequence of human genes is about 99.9 percent identical among individuals. About 1 of every 1,000 DNA bases varies among individuals, accounting for inherited differences in traits and disease susceptibility.
Changes in a DNA base sequence, called mutations, account for inherited gene variations. Mutations may be harmful if they prevent a gene from making a normal copy of its specific protein. These mutations can cause, or increase susceptibility to, specific diseases.
Single-gene diseases are relatively rare diseases that result when a person inherits one gene with a harmful mutation or a pair of genes in which each has a harmful mutation. Inheritance of these mutated genes generally results in a 100 percent chance of developing a specific disease. Single-gene diseases include autosomal dominant diseases (e.g., Huntington disease), autosomal recessive diseases (e.g., sickle cell disease), and X-linked diseases (e.g., Duchenne muscular dystrophy).
Most diseases result from a complex set of both genetic and environmental causes. Inheritance of some harmful gene mutations increases the chance, although it does not ensure, that a person will develop a specific disease. These mutations are called inherited susceptibility mutations.
Genetic testing for inherited genetic variants is performed for several purposes: diagnosis of individuals with symptoms, determination of future disease risks in asymptomatic individuals, determination of genetic risks for progeny, guidance of medical treatment, research, and individual identification.
Genetic testing for inherited genetic disease risks is an analysis of DNA, chromosomes, or gene products to provide specific information about variations in the number or form of genes or chromosomes in an individual or his or her progeny.
Genetic information is information about specific variations in genes or chromosomes learned by genetic testing or by other means.
DNA-based testing directly analyzes the DNA base sequence of a gene.
Phenotypic testing identifies specific inherited gene variations indirectly, by detecting specific variations in the structure of a protein encoded by a gene or variations in a protein's enzyme activity.
Karyotype analysis and fluorescent in situ hybridization analysis detect variation in form or number of chromosomes.
New testing technologies that will promote genetic testing in health care include DNA chip technology and tandem mass spectrometry.
Analytical validity of a genetic laboratory test is a measure of how well the test detects what it is designed to detect. It encompasses analytical sensitivity (the probability that the test will detect a gene variant it is designed to detect when present in a sample) and analytical specificity (the probability that that the test will be negative when a specific variant tested for is not present in a sample).
Clinical validity measures the extent to which an analytically valid test result can diagnose a disease or predict future disease. For predictive genetic tests, it includes positive predictive value (the ability to predict that an individual will develop a disease) and negative predictive value (the ability to predict that an individual will not develop a disease).
For DNA-based testing, clinical validity is limited by genetic heterogeneity and incomplete penetrance. Genetic heterogeneity means that different mutations in a specific gene, or mutations in different genes, are associated with the same disease. Incomplete penetrance means that within a population, not everyone who tests positive for a specific gene mutation will develop the associated disorder.
Utility of a test is a measure of how useful test results are to the person tested. Clinical utility is a measure of how a test may guide clinical decisions. In some circumstances, predictive genetic testing may not provide medical preventive or treatment options but may help reduce anxiety and/or aid planning for the future.
DNA is the most powerful tool available for identification in forensic investigations. Because of its ability to link physical evidence found at a crime scene to a single person, it is often referred to as a “digital fingerprint.” This method is so precise that it can ensure pinpoint accuracy, down to one in a billion. And, unlike fingerprints, which can only be found if a suspect touches something, DNA exists in every cell of the human body, from hair and blood to skin and tears, and can be shed or deposited while committing a crime. That means it is often the only means for accurate identification.
DNA databases make it possible for law enforcement crime laboratories to electronically search and compare collected DNA profiles to crime scene evidence. In the United States, the Combined DNA Index System (CODIS) links all local, state, and national databases and contains more than 5 million records. Currently, legislation exists on the federal level and in 29 states, enabling investigators to collect DNA upon arrest for certain felony crimes.
Genes are the blueprints of heredity. Genes are made of hundreds to thousands of DNA bases.
Each gene directs cells to produce one or more specific proteins, including enzymes and structural proteins.
The human genome is the complete set of genes that every person inherits from his or her parents. It is present in virtually every cell of the body.
The human genome consists of tens of thousands of pairs of genes. Each person inherits one copy of each gene from each parent.
Genes are organized along string-like structures called chromosomes. Each individual inherits two sets of twenty-three chromosomes, one from each parent: two sets of twenty-two autosomes and one set of sex chromosomes (X, X or X, Y).
The DNA base sequence of human genes is about 99.9 percent identical among individuals. About 1 of every 1,000 DNA bases varies among individuals, accounting for inherited differences in traits and disease susceptibility.
Changes in a DNA base sequence, called mutations, account for inherited gene variations. Mutations may be harmful if they prevent a gene from making a normal copy of its specific protein. These mutations can cause, or increase susceptibility to, specific diseases.
Single-gene diseases are relatively rare diseases that result when a person inherits one gene with a harmful mutation or a pair of genes in which each has a harmful mutation. Inheritance of these mutated genes generally results in a 100 percent chance of developing a specific disease. Single-gene diseases include autosomal dominant diseases (e.g., Huntington disease), autosomal recessive diseases (e.g., sickle cell disease), and X-linked diseases (e.g., Duchenne muscular dystrophy).
Most diseases result from a complex set of both genetic and environmental causes. Inheritance of some harmful gene mutations increases the chance, although it does not ensure, that a person will develop a specific disease. These mutations are called inherited susceptibility mutations.
Genetic testing for inherited genetic variants is performed for several purposes: diagnosis of individuals with symptoms, determination of future disease risks in asymptomatic individuals, determination of genetic risks for progeny, guidance of medical treatment, research, and individual identification.
Genetic testing for inherited genetic disease risks is an analysis of DNA, chromosomes, or gene products to provide specific information about variations in the number or form of genes or chromosomes in an individual or his or her progeny.
Genetic information is information about specific variations in genes or chromosomes learned by genetic testing or by other means.
DNA-based testing directly analyzes the DNA base sequence of a gene.
Phenotypic testing identifies specific inherited gene variations indirectly, by detecting specific variations in the structure of a protein encoded by a gene or variations in a protein's enzyme activity.
Karyotype analysis and fluorescent in situ hybridization analysis detect variation in form or number of chromosomes.
New testing technologies that will promote genetic testing in health care include DNA chip technology and tandem mass spectrometry.
Analytical validity of a genetic laboratory test is a measure of how well the test detects what it is designed to detect. It encompasses analytical sensitivity (the probability that the test will detect a gene variant it is designed to detect when present in a sample) and analytical specificity (the probability that that the test will be negative when a specific variant tested for is not present in a sample).
Clinical validity measures the extent to which an analytically valid test result can diagnose a disease or predict future disease. For predictive genetic tests, it includes positive predictive value (the ability to predict that an individual will develop a disease) and negative predictive value (the ability to predict that an individual will not develop a disease).
For DNA-based testing, clinical validity is limited by genetic heterogeneity and incomplete penetrance. Genetic heterogeneity means that different mutations in a specific gene, or mutations in different genes, are associated with the same disease. Incomplete penetrance means that within a population, not everyone who tests positive for a specific gene mutation will develop the associated disorder.
Utility of a test is a measure of how useful test results are to the person tested. Clinical utility is a measure of how a test may guide clinical decisions. In some circumstances, predictive genetic testing may not provide medical preventive or treatment options but may help reduce anxiety and/or aid planning for the future.
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