Question: How do people find other peoples D.A.N ?

Leah Fitzsimmons answered on 18 Mar 2014:

Almost all of the cells in a person’s body contain DNA (there are some types like red blood cells and nail cells that get rid of their DNA once they have finished growing). Scientists can extract the DNA from almost any type of cell and use various techniques to read the genetic code. It depends what question you are trying to answer as to what technique you would use.

Forensic scientists trying to find out who committed a crime will extract DNA from any cells they can find at a crime scene (like blood or skin) and then chop up the DNA using molecular scissors to get a pattern. The pattern is slightly different in different people – this DNA ‘fingerprint’ can then be compared to that of a suspect. This doesn’t tell you anything about what genes are within a person’s DNA, but it is a very good way to see two DNA samples are likely to be from the same person.

Doctors who want to know if someone carries a particular gene will usually take a sample of a patient’s blood to extract DNA from and then just test for the one gene they are interested in. They do this using fluorescent labels that specifically stick to a gene they are interested in and if they are looking for a mutated gene the label will be specific just for one version of one particular gene. This only tells us about one specific gene at a time.

Genetic researchers who want to look at the differences in DNA between different people – maybe comparing DNA from ancient humans and modern humans or comparing people with a certain disease to healthy people to see if a gene might be responsible – need to read much more of the genetic code to give them enough information to answer their question. In total, human DNA is made of a code 3,000,000,000 (3 billion!) letters long. Although there are only 4 letters in the code (G, A T and C), the exact order they come in is slightly different in everyone. We now know how to read the entire code (called sequencing by scientists), but it is still quite difficult and expensive, so this is only carried out where this amount of information is absolutely necessary.

Even if scientists do read the whole of a person’s DNA code, they have to keep that information private and usually anonymous, so you can only find out about another person’s DNA in special circumstances and the person being tested has to agree to it.