Short answer

Your DNA is like an instruction manual for how to build you.

Most DNA is basically the same in everyone - two eyes, two ears, one nose, etc - but there is enough variation in certain parts of the DNA that everyone turns out slightly different from everyone else.

Because of this, DNA can be used to identify individuals. On TV crime shows, detectives regularly make use of DNA evidence to match a criminal to the skin or sperm cells they left behind at a crime scene.

At DNA Labs, we are more interested in another feature of DNA - the fact that you inherit it from your parents. Knowing this, we can test related people and establish a family connection.

In the case of a paternity test, for example, if we test a child and its mother, we can compare where the two match. This tells us which parts of the DNA have come from the mother. The remaining parts must therefore have come from the father. If we look at a man's DNA and it matches those remaining points, the man is the father. If the parts don't match, the man could not have supplied the child's DNA and is therefore not the father.

DNA can also establish relationships between more distant relatives as they all will have common DNA inherited from an ancestor.

Long answer

DNA is an acronym for deoxyribonucleic acid.

This complicated-sounding name is actually a good description of the molecule. DNA is a long string of nucleotides, hence the nucleic part of the name. Each nucleotide is made up of a sugar molecule, a phosphate group and a nitrogenous base. The sugar molecule is deoxyribose.

While the sugars and phosphates stay the same all along the molecule, the nitrogenous bases vary. There are four types of nitrogenous bases in DNA - adenine (A), thymine (T), guanine (G) and cytosine (C). These four different bases combine in a variety of ways to form a code. This code contains all the information about your genetic makeup. If you were to read it, it would look something like this:

...CGTAGCTTACTTTAGGCTAGCAAACGCATC...

DNA can be further broken down into genes - short sections of DNA (though much longer than this example) that can be decoded by the cell to mean something. A single gene might be responsible for any aspect of your body's function or appearance, like making a certain protein, or the colour of your eyes.

 

                                                                                      

Long strings of DNA, twisted around each other to form a double helix and containing hundreds of genes each, coil up in the form of chromosomes. In normal human cells there are 46 chromosomes There is one pair of sex chromosomes (two X chromosomes for females and one X and one Y chromosome for males) and 22 pairs of autosomes (non-sex chromosomes) numbered 1-22.

Packaging the DNA into chromosomes ensures that the genetic material is copied and distributed evenly when a cell divides. Chromosomes can only be seen under the microscope when a cell is dividing.

 

Cell Neucleus

 

Using DNA for identification

Most DNA is pretty much the same between people - two eyes, one nose, two legs, etc - but there is enough variation to make every person unique. The uniqueness of DNA makes it an almost foolproof method of identification. On TV crime shows, detectives regularly make use of DNA evidence to match a criminal to the skin or sperm cells they left behind at a crime scene.

It is also possible to make use of the knowledge that half of a person's DNA comes from their mother and half from their father to test for possible relationships between people. In the case of paternity testing, DNA taken from a child is compared to that of its mother. Common points on the two samples show those parts of the DNA the child has inherited from its mother. Uncommon points must therefore have come from the father. When a man's DNA is tested we can see that if the points match, he is the father. If they don't, he is not.