A protocol to work on the «Cybertory» virtual laboratory at Biomodel.UAH.es Paternity testing is based on the Mendelian inheritance paradigm together with genetic diversity of individuals (genetic polymorphism). This assay specifically deals with several polymorphic regions known as STR that are part of CoDIS, which is one of the groups of international standard markers, well known because of its use by the FBI. The difference among alleles present in different individuals is in the number of repeating units and, consequently, in the length of DNA fragments that get amplified by PCR and are analysed by electrophoresis. Aim: Analysis of the polymorphic markers to ascertain which of the candidates may be the actual father of a child. The assay starts with DNA samples from each putative father, from the mother and from the child; after a PCR amplification for several STR markers, amplified fragments are separated by electrophoresis. By comparing band patterns, a deduction will be done of which candidate may be the father (or else disregard all of them).