1. What is DNA?
DNA is a chemical that occurs inside every cell of a person’s body. The DNA is contained in 22 pairs of structures known as chromosomes, plus an extra pair – the sex chromosomes – which determine whether someone is male or female. In this final pair, women have two X chromosomes, but men have one X and one Y chromosome. Each chromosome consists of two long strings of chemical letters, twisted together in the famous shape of the double-helix. The chemical letters occur in pairs as rungs on this twisted chemical ladder. The four chemical letters of the genetic code spell out instructions to the cell about how to make the proteins that allow the human body to grow and function normally. The parts of the DNA sequence that contain the instructions for making proteins are known as genes. The whole sequence is known as the genome.
2. How can DNA be used to match the deceased/unidentified person to a family member (claimant)?
DNA is useful to identify an individual because everyone’s genetic code (their genome) is thought to be unique, unless they have an identical twin. The string of chemical letters in a person’s DNA can therefore act like a unique bar code to identify them. DNA databases contain forensic DNA profiles which are not unique but contain enough information about a person’s DNA sequence to be able to identify them.
3. Why is DNA different from a fingerprint?
DNA and fingerprints can be left wherever a person goes, so both can be used to track and identify individuals. But DNA can also identify relatives, including non-paternity, and DNA contains genetic information about a person’s health and other characteristics and the risks of genetic disorders in their children.
4. What samples are taken for DNA extraction and analysis and why?
DNA can be obtained from any cell inside a person’s body. Often, blood or saliva is collected for this purpose. DNA can also be obtained from the roots of a person’s hair, tooth, tissue such as a muscle tissue and bones, sternum is the preferred choice and is only obtained in cases where the body has undergone decomposition due to drowning. The DNA inside the cells can be extracted from this tissue in a laboratory before it is analysed to obtain a DNA profile.
5. What is a forensic DNA profile?
A DNA profile is a string of numbers based on parts of a person’s DNA. Short strings of the chemical letters that make up a person’s DNA occur repeatedly in parts of the genome. These are known as short tandem repeats (STRs). The number of repeats differs between individuals and can be counted. The numbers of STRs that are used in a forensic DNA profile are different in different countries. For example, the US system (called CODIS) uses 13 STRs and the UK system (called SGM+) uses ten. Each STR is made up of two strands, one inherited from the mother and one from the father, so in the US 26 numbers are recorded and in the UK 20 numbers are recorded from the number of repeats at each STR. The DNA profile also includes a test of a gene called Amelogenin, which can be used to test whether the DNA sample comes from a male (with an X and Y chromosome) or a female (with two X chromosomes). A DNA profile is not unique, but the probability of two full forensic DNA profiles matching wrongly by chance is thought to be very low, less than one in a billion. The probability of a false match depends on the profiling system used.
6. Can my DNA help to identify my relative?
Forensic DNA profiles contain very little information about a person’s characteristics, although they can be used to identify individuals and their relatives. However, DNA samples contain a person’s whole genome and can be analysed further to obtain other genetic information. For example, DNA can be analysed to find out whether a person has a genetic disorder or is at risk of developing a genetic disorder in the future or passing a genetic condition to their children. Mutations in a gene can also sometimes mean that a person is at high risk of developing a disease in the future, even though they don’t yet have symptoms. Information from hundreds of different genes can also be combined to try to work out a person’s risk of common diseases, although these predictions are much less certain and often unreliable.
7. How will my DNA be taken?
Once an individual claiming to know the deceased has identified them through the UMID database, they can contact the police station where the case was filed at the time of death. The claimant can also contact DNA Fingerprinting lab at AIIMS New Delhi for their blood sample/buccal swab to be taken for further processing and DNA analysis. This procedure will be carried out by a professional and the claimant might be required to give some details such as
a person’s name, date of birth, address, or a copy of a valid ID, so the police and the laboratory have a record of whose DNA sample they have taken, and the database can be consequently updated.
8. What happens in a forensic laboratory?
Samples of blood, saliva, hair, tooth or other tissue from the deceased are collected from the mortuary located in the Department of Forensic Medicine and Toxicology at the time of postmortem and sent to forensic laboratory for analysis. All samples are appropriately stored in tamper-proof medical grade containers and properly labelled so that the laboratory can trace where an individual sample came from. Usually, two samples are collected from a given individual, so that one can be used for quality assurance. The DNA is extracted from the collected sample being analysed and is amplified using a chemical process known as PCR, which creates multiple copies of the DNA. The amplified DNA is separated out into the parts that are being tested (the STRs being used to create the DNA profile, plus the sex marker). A laser is used to detect the presence of different DNA fragments distinguished by their size. The data is analysed by a computer which produces the string of numbers known as STR markers that help us to match related individuals and rule out unrelated individuals.
9. How long can the police keep DNA?
Different countries have different rules about how long DNA profiles and samples can be kept. In some cases, DNA profiles and samples have been kept indefinitely, even from innocent people. In other cases, there are strict rules about what information can be stored. For example, in the UK and Germany, the spare DNA samples collected for quality assurance purposes must be destroyed once the DNA profile has been loaded onto the database, which prevents them being re-analysed to reveal private information and saves the costs of storing them. But in the US, DNA samples are stored indefinitely. In the UK, DNA profiles from innocent people were being stored indefinitely until the European Court of Human Rights ruled this was a breach of human rights. Now, more than a million innocent people’s DNA profiles have been removed from the UK DNA database.
10. How can DNA help to match the deceased with the person claiming to be their family?
DNA can be extracted from blood, semen, saliva or hair roots to obtain a forensic DNA profile. This can be compared with the DNA profiles of the unidentified body stored on our DNA database. A match between the DNA profile of the unidentified body and the claimant indicates that they are related. This information can be helpful to the family in knowing the whereabouts of the deceased before he/she passed away.