The AB0 blood group system typing remains one of the basic laboratory tasks in a forensic practice. However, problems arise when the analysed samples are seriously degraded. The DNA analysis promised to solve this but an unexpected complication was encountered. For the AB0 blood group system typing a Polymerase Chain Reaction method was used to amplify glycosyltransferase gene, when DNA had been isolated from artificially created blood stains, followed by their subsequent artificial thermal degradation. In the B0 genotype an aberrant genotype was suprisingly found and its structure was confirmed by sequencing. This meant that a newly formed B00 (not the original BO) genotype was present. Such a finding, to our best knowledge, had not been observed yet and we were unable to find any references in the professional literature. The explanation of this result thus remains unclear.

        Key words: DNA analysis – PCR – AB0 system – sequencing – aberrant genotype