It’s easy, painless and accurate. No needles.

How it is done
Geneticists take an "earbud" swab of the inside of the baby's, mother's and alleged father’s cheek. With DNA extracted from these cheek cells, geneticists can compare the baby's DNA with the parents'.

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How DNA shows who is or isn't the father
Your DNA is the same in each cell of your body. Half of your DNA is inherited from your mother and the other half from your father. This means that half of each gene-pair (there are 2 in a pair) will be from your mother and the other half from your father.

When a DNA paternity test is performed, the laboratory first compares the DNA (16 different markers, to be exact) of the child with the DNA of the mother. The more genetic locations that are examined, the more powerful and accurate the test becomes. This will show exactly which half of the gene-pairs were inherited from the mother.

Then the laboratory compares the other half of the child’s gene-pairs with the father’s genes. If it matches, the scientist can determine with statistical methods used by the South African Forensic Biology Laboratory, with 99.99% certainty, that the alleged father is the dad. For all practical purposes, this leaves no doubt as to who the dad is, explains Dr Charlotte Scholtz, from Genecare laboratories.

But, if the tested man is not the dad, the DNA will not match. The tested man can be excluded as being the true biological father of the child.

What if the alleged father is dead?
All is not lost. Instead of the DNA of the alleged father, DNA from one of the alleged father’s other children can be tested.

The Y-chromosome is the smallest chromosome of the human genome and is transmitted solely from father to son. Barring mutation, the DNA in the Y-chromosome will be identical for all paternal relatives. A boy’s Y-chromosome will be identical to the Y-chromosome of his brothers, his father, his grandfather, his great-grandfather, and so on.

If the baby is a boy, his Y-chromosome can be compared with the Y-chromosome of the dead “father's” other known sons to determine familial relationship between the two boys.

The results obtained from Y-chromosome analysis will only indicate a familial relationship between the two individuals. It serves only to indicate that they share a common paternal ancestor.

Read the full story in the latest Drum magazine.

- Health24, September 2006
 

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