A Y-STR marker test determines the number of repeats for several different STR markers. This resulting set of repeat numbers is known as a person’s Y-DNA haplotype (or Y-DNA profile).

The number of repeats for each Y-STR marker does not contain ancestral information by itself. But, it becomes useful when it is compared against other people or specific population groups. All men who descend from the same paternal lineage have the same or very similar Y-STR marker profiles.

Comparing your Y-STR marker profile against a database of populations allows you to find out which population groups are the closest match to your paternal lineage thereby uncovering your Y-DNA haplotype.