In this simulated case, the researchers are looking for DNA sequences that are only found in patients who have a particular disease.
The picture shows parts of thesequence from two different people – someone who has the disease (second sequence) and someone who doesn’t (top sequence). Can you see that the person who has the disease has a whole sequence of DNA missing?
Because the DNA sequences of each person are unique, to make sure this particular difference is related to the disease, researchers would have to see if the missing sequence is also missing in other people who have the disease, and that it is not missing in people who don’t have the disease.
Susceptibility to a genetic disease
Most diseases that have a genetic component are caused by variations in more than just oneregion. 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.