Although it sounds complicated, Short Tandem Repeat analysis, or STR, is the most commonly used technology used for profiling and forensic cases. STRs are, as their name suggests, are short, repeated DNA sequences. Each repeated sequence has 4 different base pairs per DNA.
When talking about DNA testing and specifically, relationship testing, STR technology is used to compare the loci on DNA samples. The differences in the STRs helps to determine the genetic differences between people.
When submitting a DNA test for relationship reasons, it is highly advisable that samples of all known or potential relations are provided. This will allow a laboratory scientists to separate the maternal and paternal DNA, thus giving a more accurate result.