Our body is made up of cells.
Within each cell are several compartments, including the nucleus which contains DNA.
Nuclear DNA (DNA in the nucleus) is organised into 46 chromosomes. Everybody gets 23 of their chromosomes from their mother and 23 from their father. Our combination of chromosomes is what makes each of us unique.
Two of these chromosomes are ones you have probably heard of – they are the sex-determining chromosomes, X and Y.
The chromosomes are what we inherit from our ancestors, and they are also what scientists use to analyse DNA.
DNA has a double helix shape – like a spiral staircase. The two DNA strands are complementary to each other.
This means that when the strands are separated and mixed with the right combination of ingredients, the two DNA strands can copy themselves.
Police officers can identify criminals by looking for fingerprints because each person has a different set. However, about 35 years ago scientists worked out how to read this unique DNA code that is in almost all of the cells that make up each of our bodies – and that makes us different to each other. So now, just as they use fingerprints, police officers can also use DNA to help to identify people who were at the scene of a crime.