a sequence change where, compared to a reference sequence, a range of nucleotides are replaced by a sequence from elsewhere in the genome
Format: “prefix”“positions_converted”“con”“positions_replacing_sequence”, e.g. g.123_345con888_1110
“prefix” = reference sequence used = g. “positions_converted” = range of nucleotides converted = g.123_345 “con” = type of change is a conversion = con “positions_replacing_sequence” = description of replacing sequence = 888_1110
prefix reference sequences accepted are g., m., c. and n. (genomic, mitochondrial, coding DNA and non-coding DNA)
the region converted (“positions_converted”) should start and end with a variant nucleotide
for all descriptions the most 3’ position possible of the reference sequence is arbitrarily assigned to have been changed (3’rule)
the 3’rule applies to ALL descriptions (genome, gene, transcript and protein) of a given variant
conversion in exon 9 of the CYP2D6 gene replacing exon 9 nucleotides g.42522624 to g.42522669 with those of the 3’ flanking CYP2D7P1 gene, nucleotides g.42536337 to g.42536382 from the same genomic reference sequence (NC_000022.10)
conversion replacing nucleotides g.6128892 to g.6128954 of the VWF gene (NM_000552.3:c.3675-45_3692) on chromosome 12 with nucleotides g.17179029 to g.17179091 of the VWFP1 pseudogene on chromosome 22
conversion replacing nucleotides c.812 to c.829 of the DRD4 gene with nucleotides c.908 to c.925 as in the coding DNA sequence file NM_000797.3
What is a "conversion"?
Conversions, gene conversions, result from a nonreciprocal transfer of genetic information between two sites in the genome. The two sites often contain homologous sequences, e.g. two homologous genes. The two sites can be anywhere in the genome but are in reality often not far apart on one chromosome. After a (gene) conversion event the two sites have an identical sequence.
Why not describe the variants independently?
The converted segment is usually of considerable length (several hundred nucleotides) and will contain a whole series of sequence changes. Describing these changes all independently will make the description lengthy and rather complex. In such cases it is recommended to describe the change as a conversion using "con".