Remember the day the country was hit by the Tsunami waves?….the aftermath of it?….Baby 81?…DNA analysis being used to find the true parents of the baby where there were nine of fathers and mothers each claiming that he was their baby.
So let’s look briefly into this amazing technique which is commonly used today for different purposes.
This is widely used for parental testing, forensic testing, genetic therapy and genetic genealogy. In parental testing it is used to determine the biological parents of a child. It is helpful in identifying the victims or suspects in criminal investigation and used in forensic testing. In gene therapy DNA analysis is used to test parents or fetus for genetic conditions and birth defects and in genetic genealogy it is used to find more about someone’s ancestry. The basis of DNA testing is based on the molecule DNA which carries our genetic code and determines the traits.
DNA’s double helix is a long twisted ladder and it is made of nucleotides. Adenine and thymine always bond together while cytosine and guanine pair up. Our genetic code is made up of 3 billion pairs.
99.9% of the DNA of two people would be identical while 0.1% of the code sequence which varies from the other is what makes us unique from each other.
When forensic scientists do DNA testing they use a part of the genetic sequence which is known as genetic markers. Identical twins are the only people to have identical genetic markers but closely related two will have some of their genetic markers the same. The key to DNA testing is knowing where to look in the genetic code to find the genetic markers that would be identical to a person.
Similarities in the genetic markers between two biological samples are looked for in parental, forensic and genetic testing as all cells in the body contain same DNA and samples can be taken from anywhere in the body. DNA from skin cells found under the fingernails of a victim could be compared with the DNA from a blood sample of a suspect.
In these DNA testing first DNA is isolated from the cells and millions of copies are made using the technique; Polymerase Chain Reaction (PCR). This method uses a naturally occurring enzyme to copy the specific DNA where having more DNA make it easier to analyze the genetic code.
These DNA molecules are then cut off at certain points and are separated into ‘chunks’ and the code at these specific points is analyzed to create the DNA fingerprint. These fingerprints of two different samples are compared and checked whether they do match.
The question that arises with this is “how accurate is DNA testing?”. We have seen that it is sometimes the only evidence to prove a suspect and to free someone wrongly convicted. There is always a chance of an error because if two people are related their genetic markers could be the same and this is less than one in a billion. So to reduce the errors more than one genetic marker is tested. However testing more markers occupy more time and it is expensive and in forensic DNA tests six to ten genetic markers are tested.
References: BBC Science