Paternity tests
Paternity tests are scientific analyses designed to determine the biological relationship between a father and child. They play a crucial role in establishing legal responsibilities, such as child support and access to benefits, as well as providing insight into potential inherited health issues. Historically, paternity testing began with blood group analysis; however, the introduction of DNA testing has significantly enhanced accuracy, allowing for near-certain identification of biological parentage.
Genetic testing typically involves comparing DNA profiles, which can exclude a man as a child's father but may not definitively prove paternity without additional context. For legal purposes, tests must be conducted under court supervision, while home testing kits, although accurate, are not admissible in court due to concerns about evidence tampering. The implications of paternity testing extend beyond personal relationships, impacting social and economic aspects of individuals' lives, and the technology also serves broader forensic purposes, aiding in criminal investigations and exonerations.
Paternity tests
SIGNIFICANCE: Establishing paternity can be important for establishing legal responsibility for child support, health insurance, veterans’ and social security benefits, and legal access to medical records. It may also affect a child’s future as it relates to inherited diseases.
Genetic Principles of Paternity Testing
The basic genetic principles utilized in paternity testing have remained the same from the first applications of ABO blood groups to applications of DNA fingerprinting. Available tests may positively exclude a man from being a child’s biological father. Evidence supporting paternity, however, cannot be considered conclusive. Ultimately, a court must decide whether a man is determined to be the legal father based on all lines of evidence. To establish legal responsibility, paternity tests must be administered under the supervision of the court. Home paternity tests are available, and can provide accurate results. However, these are inadmissible in court as these can be tampered with, bringing into question the chain of evidence.
The genetic principles can be illustrated with a very simple example that uses ABO blood types. The four blood groups (A, B, AB, and O) are controlled by three pairs of genes. In the example, only three of the blood groups will be used to demonstrate the range of matings with the possible children for each of them (see the table headed “Blood Types, Genes, and Possible Offspring”).
Example 1: A man is not excluded. Mother: AChild: APutative Father: AB
It can be seen that the mothers in matings 1 and 4 satisfy the condition of the mother being A and possibly having a child being A. Mating 4 satisfies the condition of a father being AB, the mother A, and a possible child being A. Results indicate that the putative father could be the father. He is not excluded.
Example 2: A man is excluded. Mother: AChild: APutative Father: B
Again, it is seen that the mothers in matings 1, 4, and 7 satisfy the condition of the mother being A and possibly having a child being A. Mating 7 satisfies the condition of a father being B and the mother A, but mating 7 cannot produce a child being A. The putative father cannot be the father, and he is excluded.
DNA Fingerprinting
After the initial use of ABO blood groups in paternity testing, it became apparent that there were many cases in which the ABO phenotypes did not permit exclusion. Other blood group systems have also been used, including the MN and Rh groups. As more blood groups are utilized, the probability of exclusion (or nonexclusion) increases. Paternity tests have not been restricted to blood groups alone; tissue types and serum enzymes have also been used.
The most powerful tool developed has been DNA testing. DNA fingerprinting was developed in England by Sir Alec Jeffreys. DNA is extracted from white blood cells and broken down into fragments by bacterial enzymes (restriction endonucleases). The fragments are separated by size, and specific fragments are identified. Each individual has a different DNA profile, but the profiles of parents and children have similarities in greater proportion than those between unrelated people. Also, frequencies of different fragments tend to vary among ethnic groups. It is possible not only to exclude someone who is not the biological father, but also to determine actual paternity with a probability approaching 100 percent.
Impact and Applications
The personal, social, and economic implications involved in paternity testing have far-reaching consequences. Blood-group analysis is cheaper but less consistent than DNA testing. Paternity can often be excluded but rarely proven with the same degree of accuracy that DNA testing provides. Human leukocyte antigen (HLA) testing can also be used but suffers from many of the same problems as blood-group analysis. The development of DNA testing after 1984 revolutionized the field of paternity testing. DNA fingerprinting has made decisions on paternity assignments virtually 100 percent accurate. The same technique has also been applied in cases of individual identification, and results have helped to release people who have been falsely imprisoned as well as convict other people with the analysis of trace evidence.
Key terms
- forensic geneticsthe use of genetic tests and principles to resolve legal questions
- human leukocyte antigens (HLA)antigens produced by a cluster of genes that play a critical role in the outcome of transplants; because they are made up of a large number of genes, they are used in individual identification and the matching of parents and offspring
- paternity exclusionthe indication, through genetic testing, that a particular man is not the biological father of a particular child
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