Genetic fingerprinting or DNA profiling is a technique which uses the individuality of DNA molecules to distinguish between organisms, or to show the relationships between them.
This technique relies on a number of quite technical processes:
The DNA is "amplified" - copied to increase the amount present - using PCR (the polymerase chain reaction).
This DNA is then then cut into small fragments using enzymes which break DNA at specific code sequences.
The resulting mixture of shorter DNA sections is separated by an electrical potential in a well-defined way by the process of gel electrophoresis.
Radioactive molecules are added which stick to some regions of DNA which are often repeated to different extents in different people.
A photographic film is left in contact with the test material so that the radioactivity will affect the film.
The film is then developed in the normal way.
The resulting genetic profiles consist of a series of bands which vary in thickness and spread out to occupy different positions.
Genetic profiling has a number of applications, including forensic science:
identification of suspects based on crime scene samples (blood, body cells, semen samples)
proving (or disproving) paternity
It can also be used to show the amount of biodiversity in an animal population in the wild, or in a zoo.
This chart shows the genetic profiles of a family consisting of a mother a father and two children.
It may be helpful if you move the mouse cursor over the diagram to get some colour-coded clues.
Compare the bands for child 1 (or child 2) with the parents. What do you notice?
> Each band is at the same position (and same thickness) as one or the other (or both) of the parents.
> Every one of the children's bands matches up to one or other of their parents.
Do the two children have the same genetic profile?
> No - they have some of the same bands but lots of differences.
What proportion of bands does each child share with one of the parents?
> Half the number
How do you explain this?
> When sperms and eggs are made, only half of each parent's chromosomes, genes and DNA are passed on into the sex cells (gametes).
> At fertilisation, male and female gametes combine and their DNA is also combined, recreating a full set of chromosomes, genes and DNA.
What result would identical twins give?
> Exactly the same- unlike prints on their fingers!