By Pius Musau

When romance goes awry leading to a disputed parenthood, or unidentifiable bodies stir a row between families, DNA testing always comes to the fore. But one needs to understand that just like all human inventions, DNA tests are not beyond reproach.

Lawyers argue that the level of evidence may be clear and convincing, but not beyond reasonable doubts. Scientifically, there are cautionary transcripts on the test results and gray areas do exist. False profiling can occur if extraneous factors are not taken into consideration.

Basis for DNA tests

Human cells contain genetic material that is donated by the two parents. The same material can be transferred to the off springs of the person and so material can be traced through generations. People who share genetic material will have them at given sites and this is the basis for the test.

The usual sequence is to have at least three runs: The initial one and two marker expansion tests of at least 16 sites. The results are such that, one to two, unmatching sites are reported as inconclusive while three or more sites are negative. The probability of parentage is zero per cent if not related (negative) and 99.99 per cent when related. Anything in between will be reported as inconclusive.

Sources of DNA

Any cellular material can be a source. Commonly, the cells of the inner cheek come in handy. Tests in the uterus rely on sampling the villi in the placenta, or amniocentesis that depends on the cells shed by the baby. Recently, home kits have been devised for people to test themselves in the comfort of their houses. Presently, it is possible to have a test using the maternal blood, in as early a pregnancy as eight weeks.

 GLANCE

Alternatives to DNA tests

The human immune system with antibodies formed against common antigens help technologists utilise the A, B and O blood typing, Rhesus factor and the antigens manifested by the white cells, as alternative ways of probable paternity test. But these have been proven to be weak in the evidence strength compared to DNA test.

Why DNA may not be conclusive

•     If the chain of custody for the material is not assured and the sample has been contaminated.

•     People with two sets of the same gene (called chimeras) will end up with a false profile.

•     Identical twins share the same genes and there would be no way of ascertaining the culprit among them.

•     If there is inadequate sample.

Doctor Musau is a consultant urologist and lecturer at Moi University, School of Medicine, Department of Surgery