Miklós Kásler - Zoltán Szentirmay (szerk.): Identifying the Árpád Dynasty Skeletons Interred in the Matthias Church. Applying data from historical, archaeological, anthropological, radiological, morphological, radiocarbon dating and genetic research (Budapest, 2021)

CHAPTER SEVEN – Genetic investigations

can be insertions, deletions and nucleotide variations. Alleles that contain an incomplete repeat unit are defined as microvariant alleles, or “off ladder” alleles (Butler 2012). Microvariant alleles are not rare: they are most often found in polymorph STR markers such as FGA, D118S51 or D21S11.

Alleles of equal length, but differing sequences

Some STR marker alleles contain variable repeating blocs, but the number of basepairs is the same as the consensus allele length. This could be an artifact and is formed during PCR amplification. This phenomenon could only be detected through sequencing (because the PCR based STR genotyping only takes the allele length as a basis), but the sequencing routine is not used in hereditary investigations.

Allele dropout and “null” (silent) alleles

During the amplification of fractured DNA strands containing STR repetitions the phenomenon of allele dropout can occur. We know that DNA sequence polymorphism can be within the repeating sequences, around the -5’ or -3’ ends of the STR, or within the primer binding sites. If the basepair swap occurs at the primer binding site, hybridization of the primer does not occur, and thus the marker on the template will not be detected. This phenomenon is called a null allele. Fortunately, this happens very rarely during routine paternity tests, as the STRs environment is stable and does not change. The danger posed by null alleles within a given laboratory does not become a problem if the same primer is used. Investigating the same 127