Before continuing, click the gray button to create the effect shown below (invisible fragments made faintly visible for clarity).

In reality, the files that you are working with are "genomic" files (as indicated by the ".gen" suffixes), meaning that the files represent the person's entire genome. The default is to show this genomic smear, but if it has been turned off you can turn this feature back on on via the "Options" menu as shown below...