Question: what is a DNA sample?

Ruth Elderfield answered on 17 Jun 2015:

DNA (DeoxyriboNucleic Acid) is found in the cells of your body and it contains all the instructions on how your body should be made. DNA carries the information that makes up our genes and whilst all humans have the genes that make them human and dogs have all the genes that make them dogs, there are very small differences within the human genes.
These very small differences could lead to a different nose shape, eye colour or even cause a disease. Some of these small differences have no effect at all.
We look at these small differences in the DNA to see if someone is more or less likely to get cancer or another disease. So a Doctor or nurse might collect a blood sample from someone and ask a scientist to get a DNA sample out of it and look at the disease gene.
The police also use DNA differences. They might find blood, hair or saliva (on a drinks can or cigarette) at the scene of a crime, they can ask a scientist to get a DNA sample to compare against a DNA database. The DNA database is made from DNA samples removed from the cheek cells of people who have been arrested by the police in the past.
We also use DNA samples to identify animals, bacteria and plants. We can use it to see how closely related to other animals, plants and bacteria they are.
DNA is very useful stuff.