DNA Testing through STR analysis looks to determine whether two persons share DNA in common compared to the population in general. The test is done through the analysis of a large number of points on the DNA (referred to as loci). The results are based on the application of statistical analysis to determine a degree of relationship.
In cases of sibling analysis, a brother and sister will of course share a lot more DNA when compared to an unrelated person. Full siblings by definition will share even more than half siblings. The DNA siblings test will therefore look at how much DNA common these siblings have and provide and indication of whether they are related or not. This type of DNA testing methodology is also applied for the aunt-uncle DNA test and the grand-parentage DNA test.
Since the STR testing is based based on the comparison on common DNA, it is recommended to submit the sample of any known parent of the individuals being tested. This will assist in separating the maternal and paternal DNA of the individuals being tested and therefore facilitate the identification and evaluation of the common DNA.
Visit interpreting the result of a DNA relationship test for more information on how to understand the result of your STR analysis.