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Molecular Biology

Paternity and Kinship Testing Information

Paternity Testing

The inherent genetic diversity among individuals provides the foundation for studies of inherited diseases, forensic investigations and the determination of paternity. Tests for paternity are based on individual genetic variability; most individuals are likely to have two different variants of a particular gene. A child will therefore inherit 50% of the genes from the mother and 50% from the biological father.

DNA profiling is currently the test of choice for disputed parentage analysis. It is extremely accurate, with the probability of paternity typically being >than 99.999%. This accuracy is based on testing the mother, the child and the alleged father. Although paternity can be excluded when only the child and alleged father are tested, a false inclusion of paternity or a statistically inconclusive result may be obtained if the mother is not tested. In this eventuality the report will not be released until the mother's blood is received. Only when the statistics are over 99.95% will the report be released as a biological match. If a result of 99.95% or higher is obtained by simply testing the alleged father and child it is NOT a legally binding paternity report. This will not be valid in a court of law. Again, the mother's blood is required to complete the family picture. Because of the reasons stated here it is strongly recommended that the mother is tested at the beginning of the process to avoid such delays and resulting in a legally binding report.

The genetic systems selected for DNA profiling are located on different chromosomes, which greatly diminishes the random match probability, as well as the influence of a blood relationship between the alleged father and the biological father. STR (short tandem repeat) loci consist of short, repetitive sequence elements 3-7 base pairs in length. The repeats are well distributed throughout the human genome and are a rich source of highly polymorphic markers, which may be detected using the polymerase chain reaction (PCR). Alleles of STR loci are differentiated by the number of copies of the repeat sequence contained within the amplified region and are distinguished from one another using fluorescence detection following electrophoresis separation. The DNA profiling test offered by our laboratory uses a fully automated system which analyses 15 different DNA loci, plus the sex determining loci Amelogenin.

If DNA matching both parents is found in the child the results are then statistically evaluated using standard statistical parameters to compare the likelihood that the alleged father is the biological father of the child against the likelihood that the alleged father is NOT the biological father of the child. If the child has genetic variants that are not present in the putative father, the alleged father is excluded from being the biological father of the child.

Kinship Analysis

Kinship analysis aims to solve the general relationship problems of which the paternity trio is the archetype. This is of use in;

  1. Inheritance disputes
  2. Deficiency case (relatives tested instead of alleged father)
  3. Sibling questions (half vs full)
  4. Incest situations
  5. Missing person problems

The DNA-VIEW software program analyses and compares arbitrary "pedigrees" or "scenarios" and makes computations, based on genetic data of the extent to which the evidence favours one scenario or another. The hypotheses generated and thus the final conclusions in the reports are based solely on the information provided by the family/ies. As it is possible that this information could be incorrect/untrue Lancet Laboratories do not accept responsibility for these results and they are not valid in a court of law. In the instance that an alleged child is to be "linked" to a deceased father the mother of the child MUST also be bled. This is a requirement, as without her DNA the statistical significance of the result can be extremely compromised. If the mother is deceased then the family tree will be assessed with Dr Turner or Dr Tsilimigras to determine who should participate.

A combination of STR loci used for paternity testing, as well as Y-chromosome analysis using markers on the Y-chromosome is used for Kinship analysis. Similar legal consents and requirements are enforced.

Y-Chromosome Analysis

STR markers on the Y-chromosome (Y-STR) have qualities that are distinct from the autosomal markers and are useful for human identification. Y-STR markers are found on the nonrecombining region of the Y-chromosome (NRY) and produce a haploid profile when amplified from male DNA. This quality simplifies male/female mixture interpretation by removing the female contribution from am amplification profile. Strict paternal inheritance of these markers makes them useful for paternity and kinship studies. Twelve different loci are amplified in the Y-chromosome kit used here.

Legal Consent

It is imperative to obtain legal consent from the parents of a minor child prior to drawing blood for paternity testing. Failure to do so could lead to legal action.

If the couple is married, both parents are considered guardians and either parent can give consent on behalf of the minor child. The original marriage certificate or certified copy must be presented as proof of marriage.

If the parents are divorced, the mother is usually given guardianship of minor children. Her consent is therefore mandatory. Should the father have been given guardianship in terms of the divorce order, a copy of the divorce order showing this must be presented.

If the parents are unmarried consent of the mother is mandatory and testing must not be carried out without her knowledge and consent.

If the mother is deceased a death certificate, or certified copy, must be presented and consent given by another member of the mother's family (ie living grandparent? or sibling).

When the child is over 18 years of age the mother's consent is not required, however, her blood is ideally requested to avoid possible inconclusive results.

In the case of kinship testing consent is required from all parties to be tested and from the next of kin of the deceased and/or minor children.

Only original identity documents/passports/driver's licenses' will be accepted as proof of identity. A birth certificate must be submitted for a minor child without identity documents.

Charges

All payments are strictly cash or credit card. No cheques are accepted and medical aid societies do not cover paternity/kinship testing.

For further information contact -

Dr C. Tsilimigras carolyn.tsilimigras@lancet.co.za
Dr. C. Turner-Babb caroline.tbabb@lancet.co.za

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