In order to know the composition of a gene sequence, researchers rely on sequencing technologies. With these tools, it is possible to know, which bases compose each gen. When we sequence all the genes and associated genetic DNA, we can get the genome. We can sequence the genome of healthy patients, vs ill patients (for example, patients with Parkinson disease or any other disease). When we have a good quality sequenced genome, we are able to reconstruct the chromosomes. At this point, we are able to gain inshight about location of the genes. Imagine that you have good quality sequenced genomes of healthy people vs ill people, in that case you could align sequences from both cases (healthy vs ill) to determine if there are changes in DNA composition (mutations, inversions, deletions, or any other rearrengement) and where it is. In essence, the mutation mapping of illness relies in sequencing alignment of suspected genes that might harbor the mutation, or if feasible the entire genomes to locate as much changes as possible. A popular tool to achieve this is BLAST, which stands for Basic Local Alignment Search Tool.