In this simulated case, the researchers are looking for DNA fragments that are only found in patients who have inflammatory bowel disease.

These DNA fragments are presented as ‘bands’ in the electrophoresis results (see the picture).

If the fragments are found only in people who have the disease, it suggests that the fragments contain the DNA from a gene variant that might mean a person is more susceptible to getting the disease.

The picture shows the results of DNA analysis from seven different people. The first lane (1) represents a ‘ladder’, which allows you to determine the size of the DNA fragments that have been separated.

Imagine that the DNA loaded in wells 2, 3, 4 and 5 comes from patients with the disease, and DNA loaded in wells 6, 7, 8 and 9 comes from people who do not have the disease. Can you see that in three of the four patients with the disease there is an extra band in the pattern?

The person with DNA loaded in lane 2 also has the disease, but the results do not show the same banding pattern as other people with the disease. This suggests that more than one genetic variation may be associated with this disease.

Susceptibility to a genetic disease

Most diseases that have a genetic component are caused by variations in more than just one gene region. Environmental effects such as exercise, diet, exposure to radiation, etc. also may have an important influence. Having a certain sequence in a region of DNA therefore does not necessarily mean you will get the disease, but it may mean you are more susceptible to getting the disease.

    Published 1 May 2006