Purpose of Parental Testing
1. Main Aim:
- 1) To establish an accurate medical history for the child.
- 2) To prevent disputes in adoption.
- 3) To create a record for immigration.
- 4) To foster peace of mind for all involved parties.
- 5) To obtain child support.
- 6) To determine the biological father or the biological mother.
2. Normally the DNA testing is for:
- 1) A woman seeking child support from a man who denies he is the child’s father.
- 2) A man attempting to win custody or visitation.
- 3) Adoptive children seeking their biological families.
- 4) People seeking to identify one parent when the other parent is absent or deceased, or desiring to identify other lost relatives.
- 5) People wanting to determine grandparentage, inheritance rights or whether twins are identical or fraternal.
- 6) People seeking entry into a country on the grounds that he/she is a blood relative of a citizen, or someone seeking to establish born rights.
- 7) Those who have received inconclusive results from other methods or who want a second opinion.
- 8) Criminal cases related, such as a rape, homicides and incest.
Following menthods are used for paternity testing
- ABO blood group typing,
- analysis of various other proteins and enzymes,
- using human leukocyte antigen (HLA)
- DNA testing
I. The two most important classifications to describe blood types in humans are ABO and Rhesus factor (Rh factor). In cases when paternity is questioned, ABO blood-typing can be used to exclude a man from being a child’s father. For example, a man who has type AB blood could not father a child with type O blood, because he would pass on either the A or the B allele to all of his offspring.
II. The HLA test is a test that detects antigens on white blood cells. There are four types of HLAs: HLAA, HLA-B, HLA-C, and HLA-D. The HLA test provides evidence of tissue compatibility typing of tissue recipients and donors. It is also an aid in genetic counseling and in paternity testing. HLA is a substance that is located on the surface of white blood cells. This substance plays an important role in the body’s immune response.
III. DNA Markers and paternity
1. DNA testing with PCR: In the PCR method of testing, DNA is first isolated from the sample. Individual gene fragments are then synthetically produced in the laboratory and
they are labeled with special fluorescent tags. These fluorescent tags enable detection of the genes.
2. DNA testing with STR: STR markers are polymorphic DNA loci that contain a repeated nucleotide sequence. The STR repeat unit can be from two to seven nucleotides in length. The number of nucleotides per repeat unit is the same for a majority of repeats within an
STR locus. The number of repeat units at an STR locus may differ, so alleles of many different lengths are possible. Polymorphic STR loci are therefore very useful for human identification purposes. STR loci can be amplified using PCR process and the PCR products are then analyzed by electrophoresis to separate the alleles according to size. PCR amplified STR alleles can be detected using various methods, such as fluorescent dye
labeling, silver staining, or fluorescent dye staining.
3. DNA testing with RFLP: In the RFLP method of testing, the DNA isolated from the sample is cut into fragments by DNA restriction endonucleases. Then, an electric current is used to separate DNA fragments by size. The separated DNA fragments are identified with DNA probes. These probes are pieces of custom made DNA that bind and identify a specific gene locus.
1. Extraction and purification of DNA. The sample is treated with chemicals to break open the blood cells. DNA is separated from the cells and later purified.
2. Cut DNA into fragments. Enzymes that recognize certain sequences in the chemical base patterns are added to the DNA. These enzymes act like molecular scissors and cut the DNA molecule at specific points, leaving fragments of various lengths.
3. Sort fragments by length. The DNA fragments are placed on a gel, and an electric current is applied. The DNA, which is negatively charged, moves toward the positive end, the smaller fragments moving faster than large ones. Hours later the fragments have
become arranged by length.
4. Attach probes. The nylon sheet is immersed in bath, and a probe – a DNA segment of known sequence – is added. The probe targets specific base sequences and bonds to them.
5. Make a print and analyze it. X-ray film is exposed to the nylon sheet containing the luminescent labeled probe. Dark bands develop at the probe sites.
Ethical, Legal and Social Issues (ELSI)
- Communicating Test Results- written consent.
- Duty to Disclose- implications for family members, hence not to inform other family members without the permission of the person tested, except in extreme circumstances
- Genetic Discrimination- people should be aware that the results could be accessible to others.
- Informed Consent- informed consent is an important part
- Privacy- enormous implications for the individual and the family
- Psychosocial Impact- refrain from judgment
- Societal Values- questions about personal responsibility, personal choice treatment.
Test Validity- measured as test specificity, sensitivity, and predictive value.